Obvious mudding and damage in a wall - Note the depressed section around the mud where the termites have eaten out the plasterboard.
If you see mudding around an architrave or wall, then you probably have termites! It may not be as obvious as this, so that's why it's good to get regular inspections. Usually, when the termites are this obvious, there is a fair bit of damage done underneath.
Termites may cause mudding on the wall like this in preparation for a colonising flight. The termite colony releases many winged reproductives called alates. These are usually dispatched from a higher location on a mild evening during the spring and summer months, typically when there is high ambient humidity. So if you see many of these swarming inside your house, you know that the colony has already found it's way in!