I've had Hermanns for many years but I've never seen a penis in real life - let alone such a behaviour. :eek: I also have quite a few aquaintances with male Hermanns, they were shocked when I showed them pictures. :D Maybe Hermanns are less "hormonal" than some other species?
Oh. :D That looks like paint residues to me. Most breeders mark their babies shells (with numbers or whatever) to keep them apart and of course they use some kind of marker that is very resilient and hard to rub off. Just let it be, I bet it will disappear little by little over time.