I realised this isn't a creative question at all. It's a media and targeting one, as the brief contains a bad assumption. Since your target audience is squash players, the sign shouldn't go at the pool entrance, but rather at the squash courts.
There are good reasons to move the sign. But often, clients don't like it when you do.
First, you regularly find you are presenting your work to the swimming pool manager, who has no authority to put up signs in the squash courts. Worse still, in the client world, the pool manager and the bloke who runs the squash courts often hate each other.
Yet a bigger problem may be psychological. There's a feeling that, if you brief someone to come up with a press campaign and they present a solution involving text-message reminders, they are somehow cheating.
This issue isn't confined to the ad industry; take John Harrison and the £20,000 Longitude Prize. The great clock-maker was in his eighties before he was rewarded for his contribution, but he never received the whole prize. Why? Because the board wanted an astronomical solution to the navigation, not a horological one. Harrison's clocks were seen as a cheat, because while they solved the problem, it wasn't what was expected.