There are several points here:
1. If the restaurant has posted the incorrect sign, you can tell by looking at their actual license. If on the license it says "License = Blue" they are not 51% and you can carry in the establishment regardless of how they've posted. If it says, "License = Red", then they are 51% and you cannot legally carry in the establishment.
2. In Texas, the law regarding prohibition on CHL holders to not carry in places that receive 51% of their REVENUE (not profit) from alcohol sales for CONSUMPTION on the PREMISES is just that. It doesn't matter what sign they have posted -- it is up to the CHL holder to know whether it is, or is not, a 51% establishment, and the only positive way to tell is to look at the license itself.
3. As of 01 September, 2009 it is a defense to prosecution that the business did not properly post its 51% sign if they are, in fact, a 51% establishment. This doesn't mean a CHL holder won't be charged for carrying in a 51% establishment when that business failed to post the warning sign or posted the incorrect sign, but he can raise it as a defense during trial, and should be acquitted. That doesn't help in this case because it is the converse instance. The business posted 51% when they are not, likely, actually a 51% business.
Finally, if the business is posting the incorrect sign, you can contact the TABC. They will send an agent to the establishment and force them to post the correct sign consistent with their actual license. My guess is that this place doesn't want the big ugly 30.06 sign on their front door, so they chose to post a 51% sign instead. Or, even more likely, the TABC sent them a packet of all the signs, and someone picked the wrong one from the box.