Y'know, I think the Sins give their significant others tattoos that help protect them (and allow them access to otherwise blocked off areas and circles), and show their status. Just look at Vortex:
His tattoo looks like the emblem for Beelzebub. And Fizzarolli:
I'm pretty sure the main one is the one on his forehead (possibly replacing the (maybe) slave tattoo that him and Blitzo's family have/had?), but he has hearts all over his outfit, further showing that he belongs to Asmodeus.
Having said that, I'm pretty sure Alastor would get one as well once he begins dating Lucifer, perhaps on the back of his hand? (All of the other spots seemed to be on places easily noticeable/accessable.) Lilith probably had Lucifer's emblem as well, tho she most likely removed it when she left. I'm guessing It'll look like one of these: