There are many schools of thought on a discount.
One being..... don't give anything up, unless you have to. Good sound business advice.
However, my take is.... beat 'em to the punch. Don't wait for them to ask. Offer it to them and create an image which will form a most favorable reputation. As OP said, give yourself a little play, so you can give a discount, but not so much if they price around, you're still in line with everyone else.... or the jig is up.
Wanna do fleet work ?? Wanna do lots of fleets ?? Wanna be busy year round with the easiest and most lucrative part of the sign business of all ?? Offer incentives, do top quality work and they'll be flocking at your doors in no time. Ask me how I know.