Can they keep you out because you legally carry just by posting a sign? I don't think they can do that for any other reason. What if a business put a sign in the window that said "No Gay People Allowed"?
I'm just asking here as I don't actually know.....
Under the law that was modified in the last session of the Texas legislature, knowingly walking past a proper 30.06 or 30.07 sign with a licensed handgun either concealed or openly carried was reduced to a class C misdemeanor with a potential punishment of $200 which will not result in the loss of one's "License To Carry a Handgun" (LTC), formerly a Concealed Handgun License (CHL). Failure to depart the premises when instructed by an employee with authority to do so remains a class A misdemeanor which is a serious offense and your LTC would be suspended pending completion of the legal process. Conviction of that offense would result in revocation of a LTC and disqualification from applying for one for five years.
The sign described does not comply with the requirements of Penal a Code sections 30.06 or 30.07. There are also various alcohol related signs to be on the lookout for, most notably a red 51% sign which makes it unlawful to carry a handgun into that establishment. This can be a very serious offense.
Many people and groups encourage sending letters or emails to the corporate headquarters of businesses which post the 30.06 and 30.07 signs registering your complaint so that they know that they have lost business because of their choice.
Some groups have business cards, such as this one which has talking points on the back, to use when speaking with a store manager (after leaving your handgun in your vehicle). I don't know if posting the kink to the cards is allowed, Wilbur, so please delete it if it is not appropriate.
http://shop.opencarrytexas.org/No-GunsNo-Money-Cards-50pk-NoGunNoMoney.htm
There is a website which lists businesses that have posted signage.
https://www.texas3006.com
There was a mention of Luby's Cafeterias elsewhere. Many will recall that a Luby's was the site of a terrible shooting a number of years ago at which Suzanna Gratia-Hupp's parents, among others, were killed. Both they and Fuddruckers hamburgers are owned by the same company which is headquartered in Houston. The corporate headquarters were actually quite rude when an inquiry was made.
The answer to your question about a "no gay people" sign is they are a legally protected class of persons and we, with our handguns, are not.
Rick
P.S. According to the most recent statistics from the Texas DPS, the offense rate for LTC holders is 0.3% which is less than that of commissioned peace officers (about 2% according to the FBI). This simply illustrates that both are very law abiding groups of people.