There are definately pads for men too, marketed under trade names like MEN and sold in pharmacies.
However, this only solves the problem if you are able to mention it to the man.
I would hesitate to mention the matter, but might do so if the man in question is a widower, or living alone for other reasons.
If he is married, it is a matter for his wife to deal with, and if he has carers coming in, it is up to them.
If you feel you must mention it, best perhaps just to say, "Excuse me, but I couldn't help noticing that you have stained the front of your trousers."