Well St. Expedite brings only speed to most endeavors. Most saints require some kind of regular devotion if you want their influence to continually manifest. This doesn’t mean you need to do daily prayers and offerings, but setting up an altar for him would be a good start. You could get a statue or image of him plus a non-perishable, corresponding item that he likes.
As far as the offerings go you can give one item or many items; and they should always be given after you have witnessed results. With that being said, it is a good rule of thumb to give a glass of water while petitioning and waiting for spell results.
After he does his work then you would want to give him a nice slice of pound cake (cut from the middle ). If you want to, and can afford it, can you also include some flowers as well.
But jsyk, if you are in dire needs the saints understand this. A glass of water will suffice if that is all you can afford.
After a few days, but before the cake molds and the flowers die, put the cake outside for the animals. You can just leave the flowers in nature if you like.
As far as asking him for a signal I would say, why not? Saint Expedite works pretty quick so usually the end result manifesting IS the signal.