SOMAD is the user ID.  This is how EROS ads work for the most part.  NY is the city location, followed by the user id, followed by the ad name, followed by picture id.  There are exceptions, generally to girls that travel or are well known.  It can be either city id or us (ny-ginger1 or us-ginger1) followed by picture id.

Some girls use an agency to place ads for them, and that is what "SOMAD" is, or at least my understanding.  If you noticed, my T's that visit NYC and know Allanah Starr, use her id to place an ad, for example:

Allanah Starr's Ad:

http://www.eros-ny.com/files/ny-allanah1-allanah1.htm

Julie's Ad (visiting til 10/28):

http://www.eros-ny.com/files/ny-allanah1-julie1.htm

Another example, Nastia Kossonova Ad (visiting til 11/3)

http://www.eros-ny.com/files/ny-allanah1-nastia1.htm

That is my understand from past posts on this and experience.  Another one in NYC is "bellas".  I hope this clear it up.  Maybe one of T-Girl contributors can shed more light on the subject.