To operate the flush system, press button and then release.
Personally, I'd word that as:
To flush, press button.
Are people being taught this in school these days? Never be concise. Add extraneous detail. Ramble. There's a lot of it about.
I especially like the "and then release". Without that instruction, how many people would end up stuck in the toilets, endlessly flushing?
For sheer poetic bizarrity, though, that sign is trumped by the one they've stuck on the hand driers in the Stranraer terminal:
Move hands and comfortable hot air will be sent out automatically.
I can't even decide whether that's stupidity or genius.