In addition to the other things listed above;
Comments about 'hayfever' or 'a bit of a cold' when nothing's in flower, not even trees and nobody else has a cold and his disappears by the next day, only to return a few days later. Sniff...sniff...sniff...oh, this hayfever...sniff...sniff.
Very keen to pop to the shop for you, so keen that he'll practically run out of the door, almost shoving you aside even if you've got your coat, shoes, handbag and the keys in your hand.
Your handbag isn't quite where you left it and your phone case/card holder/purse is never in the same pocket of your bag/coat.
Check your bank account. There could be two cash withdrawals immediately after one another or a cash withdrawal and then the intended supermarket purchase straight after.
Anything portable and sellable go missing? Like computer games, old phones, a piece of jewellery you don't often wear?
The biggest one is that they're an irritating cock, though. Well, more than usual, at any rate.