If a postmark reads "S Suburban MD P&DC 208" , where is this located?

jafo100 --

The postmark indicates that the mail was processed by and sent from
the Suburban Maryland Processing and Distribution Center, which is
located  at the following address:

16501 Shady Grove Road Gaithersburg, MD 20898 
Tel: 301-670-6000

Here is a link to an online source for that information:

Gazette.net: Montgomery County: Post Offices
http://www.gazette.net/200428/montgomerycty/community_guides/227834-1.html


Search Strategy:

I used part of the postmark as search terms for this Google search
that led to the information:

"suburban maryland P&DC"
://www.google.com/search?num=100&hl=en&lr=&q=%22suburban+maryland+P%26DC%22&btnG=Search

I then used the following Google search to establish that P&DC stands
for Processing and Distribution Center:

P&DC center
://www.google.com/search?num=100&hl=en&lr=&q=P%26DC+center&btnG=Search


I am confident that this is the information you are seeking, and I am
happy to be able to give you an answer promptly.  If anything is
unclear, please ask for clarification before rating the answer.

markj-ga