The amount on the cash register behind the clerk changes from five cents to ten cents as the duo are getting ice cream.
Stan signs his name on the little door, below the note he has written, on the door to Ollie's apartment. Then when he opens the little door himself, his signature has disappeared.
When Stan signs his name on the note look carefully on the door. You can see a marking which bears a similar resemblance, which would indicate a previous take.