hi, thanks for messaging me! it’s awesome that you’re asking someone if you’re not sure instead of risking accidentally being offensive =)
honestly, there are lots of opinions in the Deaf community about this. some people say it’s ok to start signing, and others say it’s not. it really depends on the individual. if you want to be the one to initiate conversation, i would suggest speaking first to him, and if he responds back, ask if he signs and if he would rather communicate via sign or a different medium. it really does depend on the person, i think. like i said, some people become very offended over someone approaching with sign, and others are pretty indifferent.
as long as you show respect and the willingness to try to communicate, no matter the medium, that’s the best you can do =)