Some galas require the swimmer to sign in once you have arrived at the pool. On arriving the swimmer should ask where the signing in desk is, check their name against the lists on the desk and sign. If your name is not on the list you should see your coach immediately. If a swimmer does not sign in they will not be able to compete.
Similar to sign ins, some galas operate an entry card system. Cards will be sent out by the organising club prior to the meet and given to you by your coach. Usually there is one card per event with details of the session and warm up time plus your name, club, entry time, etc.
At the gala, the cards have to be posted by a set time before the session starts or you will be deemed a non-attendee and will not be able to race. There is usually a card post box near the entry desk or changing area to post your cards.