The Clathermonts

"Letters in and out of the city are routinely read. But one does not often intimately search a gentleman, and never a lady. So, the rumour has it, Clathermont and his three glum-faced tattooists - triplets, who some say are his daughters - although some hint at a more intimate relationship - hm - where was I? Ah yes. The rumour has it, spies come to Clathermont's to have messages tattooed in less public areas of their skin. This has, of course, been responsible for a scandalous vogue for secret tattoos."

Clathermont himself, as seen in SS.

Mr. Clathermont and his tattoo parlor, which is in the vicinity of Ladybones Road, are featured in both Fallen London and Sunless Sea. 

Residents of London may get any number of small Great Game-related tattoos at Mr. Clathermont's parlor, provided one has enough connections to the Great Game to find him. During the Feast of the Exceptional Rose, residents can also let Mr. Clathermont's wife Millicent give them tattoos. (By the way, Clathermont's triplet tattooists, mentioned in the snippets above, are named Edie, Myrtle, and Lily.)

A tattoo from Clathermont's - a secret symbol of the Great Game.

Millicent Clathermont, also known as the Lady in Lilac or just "Lilac", also travels the Sunless Sea; she often appears when a crew is frightened out of its wits. She has another daughter - not Clathermont's - who calls herself Maybe's Daughter.

Maybe's Daughter's father isn't human;...
...he is one of the cats who are the enemies of the snakes (the Fingerkings) in Parabola.