George loses his watch someplace in the large office building where he works.  He posts an sign in the lobby that says: "Help! I lost my watch!  It is gold and says "George" on the back. I promise to pay $400 to the first person who finds my watch and returns it to me."  Donna, reads the sign, starts looking for the watch, and finds the watch in the office mail room. 

Donna accepts George's offer the moment she finds the watch.

Donna accepts George's offer the moment she reads the sign and starts looking for the watch.

Donna accepts George's offer only when she returns the watch to George.

George's sign is not an offer.