The caricature refers to the Carlsbad Decrees, which were implemented at the behest of Clemens Prince von Metternich. The decrees suppressed (national/liberal) student fraternities and imposed tight restrictions on freedom of expression. Contemporary lithograph mocking the new restrictions on the press and free expression. The sign on the wall behind the table reads: <i>Important question to be thought about in today's meeting: 'How long will we be allowed to think?'</i> The sign in the upper-right corner lists the rules of the Thinkers' Club: <i>I. The president opens the meeting at precisely 8 o'clock / II. The first rule of this learned society is silence. / III. So that no member may be tempted to let his tongue run free ... muzzles will be distributed upon entry. / IV. The subject which through mature reflection shall be thoroughly expounded at each meeting, is written in distinct capital letters on a board. / V. Each member of this society ... [ text obstructed from there ]</i>
The original uploader was <a href="https://en.wikipedia.org/wiki/User:Auntieruth55" class="extiw" title="wikipedia:User:Auntieruth55">Auntieruth55</a> at <a href="https://en.wikipedia.org/wiki/" class="extiw" title="wikipedia:">English Wikipedia</a>.
<i><a rel="nofollow" class="external free" href="http://germanhistorydocs.ghi-dc.org/sub_image.cfm?image_id=427">http://germanhistorydocs.ghi-dc.org/sub_image.cfm?image_id=427</a>  Also, Michael Behnen, "Deutschland under Napoleon, Restauration und Vormärz," in </i>Deutsche Geschichte, von den Anfängen bis zur Gegenwart,<i>  Martin Vogt, Her.  Frankfurt, Fischer, 2002.  page 426.</i>)