I'm not good on his early signature, but I've seen that signed lithograph being sold through Bonhams before. The signature however is in the left margin and appears to be in pencil. I don't know if this was an additional run or what the deal is.
Thanks BC, I also have seen this lithograph sold by Sotheby's but was also signed in pencil and to the left hand margin. I will put a separate post up for further help on this in hope someone can shed some light if another run were signed in pen or not.