Egyptian 505?
Caecilia?
Silica?

hhp

By the way - to me this marks reads either as 4P or HR, but not as HP.

If the bottom left stem of the H wasn't broken I'd see HP alright. The break makes the P look like an R with a break too. Also the broken H makes all the negative space very busy and distracting for what are actually very solid, sturdy letters.

I also saw "HR".

- Lex

HR here as well... Because both lack part of a letter...
___________
Robert Koritnik

I am just left wondering why there are missing parts and then added parts.