Note that some places in TX don't require a sign to prohibit concealed carry - these include polling places during an election, a court of law, the secure area of an airport, a correctional facility, etc. (See Texas penal code section 46.035) A TX CHL doesn't exempt you from laws governing Federal facilities, either.
Amusement parks above a certain size (Six Flags lobbied for this one) and public sporting events are off limits even if they are not posted.
Well, just to nit-pick a little . . .
Section 46.035 section (b)(5) states that amusement parks are off limits to licensed concealed carry.
Amusement part is defined in section (f)(1) of the same statute as ". . . a permanent indoor or outdoor facility or park where amusement rides are available for use by the public that is located in a county with a population of more than one million, encompasses at least 75 acres in surface area, is enclosed with access only through controlled entries, is open for operation more than 120 days in each calendar year, and has security guards on the premises at all times . . . "
Seems pretty clear, but if you keep reading the statute an exemption is spelled out in Section (i) which says that "Subsections (b)(4), (b)(5), (b)(6), and (c) do not apply if the actor was not given effective notice under Section 30.06."
So the law prohibits concealed carry in the amusment park, but the prohibition doesn't apply if notice isn't given.
I've read that Six Flags has in fact posted compliant PC30.06 signs at the entrance - so as long as the signs are up, notice is being given, which for law abiding folks pretty much puts Six Flags in the same category as any other business posting a compliant PC30.06 sign.