Definitions of "bulletin board" I could find in English:
https://en.wikipedia.org/wiki/Bulletin_board

https://dictionary.cambridge.org/dictionary/english/bulletin-board
a board on a wall for putting up notices
noticeboard
noun [ C ] UK
UK  /ˈnəʊtɪsbɔːd/ US 
(also message board); ( US bulletin board)
a board on a wall on which pieces of paper containing written information can be fixed:

https://www.merriam-webster.com/dictionary/bulletin board
a board for posting notices (as at a school)

https://ejje.weblio.jp/content/立て札
立て札を立てる
put up a notice 《reading…》.
「芝生に入るべからず」という立て札が立ててある. There is a notice [A notice has been put up] reading ‘Keep off the grass.'

下馬札という立て札
例文a posted notice requiring riders to dismount

https://ameblo.jp/englishtoday/entry-11143673032.html
本The origin of the closed gate was explained in a notice.
サーチ閉ざされた門の由来が立て札に書かれていた。 (with picture at link)

Instructive google image search results:
"立て札" "神社"
"立て札" "公園"
"立て札" トレール　        立て札 in the middle of the woods
"立札" "花"　　　       （you can stick a 立て札 *in* a flower pot!)
"立札" "イラスト"
(the signs are only blank so you can add your own text, not so you can pin bulletins to them)

Got here from 辻札.  I see an attempt was made 10 years ago to remove "bulletin board" from this entry.  I'd like to revisit that conversation.  I suspect this is an issue about English more-so than Japanese.

Without a doubt, these signs are bulletins, and they are often carved/painted onto pieces of wood ("boards"), but I don't think we should gloss bulletin + board as "bulletin board" because this has very clear, readily understood meaning in English (掲示板).  

If you look at reverso, the only translations that use "Bulletin Board" are hapless J->E translations that are relying on the accuracy of this very gloss (From GG5, 新和英中辞典, ルミナス, Eijiro, or wherever). And the translations are poor. (They are using this gloss because there *is* no particularly good gloss available. )

I completely agree with Nil's comments from 2013 that the current gloss of "bulletin board" is extremely misleading, in both J->E and E->J directions. It serves basically no purpose.

"Billboard" has the exact same problem:
https://en.wiktionary.org/wiki/billboard
A very large outdoor sign, generally used for advertising. 
(dated) A flat surface, such as a panel or fence, on which bills are posted; a bulletin board.

"notice board" is effectively a synonym for bulletin board. (image search confirms).

These signs also need not be roadside.  (They may be roadside, because that would be an obvious place to put them, but they could be at the entrance to a shrine, inside a shrine by some statue or tree, inside a flowerpot(apparently)).

Really there is very little magic here.  This is just a 札 on sticks (立て).

And this is very common term in Japanese, so I think it's worth reflecting on.
立て札	88505	73.0%
立札	32764	27.0%

Just noticed there is an entry for 高札 with an xref into English. No effort is made to gloss it literally. They use "public notice" which matches the various glosses of "notice" I also encountered. 
https://ja.wikipedia.org/wiki/高札
https://en.wikipedia.org/wiki/Kōsatsu
Kōsatsu
The Kōsatsu (Japanese: 高札, literally "High plaque"), also called Seisatu (Japanese: 制札, literally "Controlling plaque"), was the public notice of the han-lord's or shogun's proclamations in the Japanese history.[1] They were the local or nationwide laws written on the wooden plate,...


You can inspect for yourself at reverso. Every entry using any of our glosses is in grammatically incorrect English.
https://context.reverso.net/translation/japanese-english/立て札

Good translations:
勝利の立て札を持って I am carrying a victory sign 
This area is posted with no trespassing signs.

You'll find signposts outside temples denying the entry of menstruating girls and women.

In public places, especially intersections and riversides where people easily gathered, notices would be put up, 

左端の立て札には金亀楼（きんきろう） The sign on the left says "Kinkiro,"

@@ -23,5 +23,3 @@
-<gloss>bulletin board</gloss>
-<gloss>notice board</gloss>
-<gloss>billboard</gloss>
-<gloss>roadside sign</gloss>
-<gloss g_type="expl">sign on a post, usu. wooden, esp. containing information about a sight, warning, congratulations, etc.</gloss>
+<xref type="see" seq="1298970">札・3</xref>
+<gloss>sign on a post (usu. wooden, oft. with a small roof, esp. containing information about a sight, warnings, congratulations, etc.)</gloss>
+<gloss>public notice (on a sign)</gloss>

@@ -27,1 +27,1 @@
-<gloss g_type="expl">sign on a post. usu. wooden, esp. containing information about a sight, warning, congratulations, etc.</gloss>
+<gloss g_type="expl">sign on a post, usu. wooden, esp. containing information about a sight, warning, congratulations, etc.</gloss>

GG5, Daijr, 新和英中辞典, ルミナス, Eijiro

I think this works better.

@@ -23,2 +23,5 @@
-<gloss>sign (on a post) (generally wooden, esp. information about a sight, warning, or congratulation)</gloss>
-<gloss>roadside sign (often with small roof)</gloss>
+<gloss>bulletin board</gloss>
+<gloss>notice board</gloss>
+<gloss>billboard</gloss>
+<gloss>roadside sign</gloss>
+<gloss g_type="expl">sign on a post. usu. wooden, esp. containing information about a sight, warning, congratulations, etc.</gloss>

daijr koj shinkaisan

This has a few very specific meanings; see Google image 
results. It’s basically “wooden sign on a stick”
Firstly, it’s a casual term for the ubiquitous roofed wooden 
roadside signs that have been around since antiquity and are 
these days distinctive of Japanese tourism. (The formal term 
is 高札, and that’s given as a synonym.)
Secondly, it’s used for some other wooden signs on posts – 
general warnings, and お祝い

“bulletin board” is extremely misleading (that’s instead 掲
示板), and “notice board” is little better, as these suggest 
boards that one sticks notices to (esp. paper notices), but 
in all examples I’ve seen these are permanent printed signs. 
Perhaps these can be used in this sense in English, but it’s 
v. confusing.

Glossing this usefully is a balance between specificity of 
use and not getting encyclopedic; I’ve linked to 高札 for 
the history.

@@ -22,3 +22,3 @@
-<gloss>notice</gloss>
-<gloss>sign (on a post)</gloss>
-<gloss>bulletin board</gloss>
+<xref type="see" seq="1808810">高札・1</xref>
+<gloss>sign (on a post) (generally wooden, esp. information about a sight, warning, or congratulation)</gloss>
+<gloss>roadside sign (often with small roof)</gloss>

大辞泉 大辞林
http://dic.yahoo.co.jp/dsearch?enc=UTF-8&p=立て札&dtype=3&dname=2na&stype=0&pagenum=1&index=02608800

@@ -23,0 +23,1 @@
+<gloss>sign (on a post)</gloss>