Ballbusting doesn't typically cause marks, especially if you keep it moderate. Maybe keep away from the implements.

Electricity is the gold standard for pain without marks.

Might sound counterintuitive but needles can actually be really good for this, leaving extremely tiny subtle marks that go away very quickly. Stick to thinner needles on the underside of the penis and the ballsack, avoid the head, and don't do dick needles if your balls are in a vice.

People are hugely variable in how prone to marks they are. If you suspect you bruise easily, it's a good idea to let the Mistress know.