BART signs/markers

Hey everyone! I'm a really big BART fan and I was wondering if you could help me out with a definition of what the following signs found on BART tracks mean...thanks!

Every few feet there are blue signs with white writing that say things like:
24 56 W2...

The small yellow square signs that say stuff like W 45 D...

White signs that say "M 90 1000"

Enter TM 1 (or any number), Enter TF 01 (or any number), Enter Stage Make 7 (or any number).

And finally the diamond signs (yellow) that have these on them:

"G", "CS", "S" or "P".

I've also noticed along the Alameda line diamond yellow signs with numbers like "30" on them...if anyone can give a definition of what all the above signs mean...that'd be GREAT!!!

"Every few feet there are blue signs with white writing that say things like:
24 56 W2... "

Mileposts, we assume. MP zero for the San Francisco line is the north end of the Oakland wye, for the Richmond/Concord lines is the east end of the wye, and for the Fremont line is the southwest end of the wye.

"White signs that say "M 90 1000""

Presumably 1000 feet to the center (?) of the platform at the ninth station on the M line-- that would be Balboa Park maybe?

The yellow speed-restriction signs seem to show the upcoming reduced speed first, then the "S" marks the actual start of the restriction.

What about the "P" signs? I talked to a train operator about the mile signs and he said it's the distance from the Oakland Wye (24 50), the line (W), and what track (2). He also told me that there are the: A, C, M, L, R, W and Y lines. They stand for:

A- alameda
C- contra costa
M- metro
L- livermore
R- richmond

I don't know what the W and Y lines mean...the W starts at 16 3 before Colma and continues past Millbrae ending at 24 7. The Y line is for the SFO station tracks. Don't know what the letters mean. The "G" signs mean a gate is coming up one train-length ahead, and "CS" means that the train has cleared the gate. The operator was nice enough to tell me what those meant. The "W 45 D" are the gate markers the W is the line, 45 is designation on the line, and D is an alpha code. Also, the ENter TM signs mean terminal zones..that's where the trains can be dispatched by the control center. My my how informing the operators are.