There are some Shell convenience stores in the Houston area that are posted with a 30.06 sign, but it probably isn't legal. It is printed in white on the front glass window. You can barely see it.
Other ones I have seen have been at certain entrances to the Galleria, but not all of them are posted.
The Medical Center has a lot of them, but not at all entrances.
Other than these few, I have rarely seen one.