Franking question

I have a letter written in November of 1844, posted from Washington,
D.C., with a franked signature that appears to include the last name
"Benjamin" (with first initial "R" or "P" or "J" or "S"--difficult to
tell). The author of the letter is a young woman (her signed name,
perhaps a nickname, is indecipherable) but from the internal evidence
of the letter my guess is that she was the daughter of a high-ranking
naval officer or other official involved with the Navy. My
understanding (open to correction) is that naval officers and other
government officials had fairly wide franking privileges.
Unfortunately, I have not been able to identify a contemporaneous
naval officer with the last name of "Benjamin."

Hoping that this is not too far off topic, but can anyone point me to
resources on franking, particularly some that might help me identify
who franked the letter (and ultimately who was the author of the
letter)?

nomilk