I was sold a card by a beggar at a Dunkin' Donuts in Baltimore, Maryland last year. Here are the letters - they can be used when one does not know the specific sign for a given word or concept, or when there does not exist a sign for it:
A                     B                         C
                       ,,,,
                       ||||                        ___
____                   ||||                         \\\
||||\                  |  /\                     |\_/ /
\^^^/                  \  ^/                      \  /
 | |                    | |                       | |
(clenched fist)        (extended palm)           (C-formed fist)


D E F ,, ,, ,,,, || _____ \\ |||| ____|| ||||| \\||||_ ||// | |^^__| \ //| \^\`-| \ ´´/ | \`| | `/ | | \ / (D-formed fist) (clenched fist) (OK-sign) (with thumb underneath) (with spread fingers)

G H I ,, ||___ ________ ________ ||||| `^^^=__ \ `====__ \ |^^__| \ \/ \ \/ \ ´´/ | | | | | | (pointing hand) (pointing hand) (clenched fist) (with two fingers) (with little finger up)

J K L ,, ,, ,, ,, ||___ | \\ // || ||||| | __\\// __|| |^^__| ´|` | |||/\ ||| \___ \ ´´/ \__/ \^^^/ \^^ /^^´ | | | | | | (same as i) (Victory sign) (Form an L) (but move as a J) (with thumb in front)

M N O ___ ____ ____ //\\\ <|||\ |<||\ |\/ / \^^^/ \^^^/ \ / | | | | | | (clenched fist) (clenched fist) (O-formed fist) (with 3 fingers on top)(with 2 fingers on top) (of the thumb) (of the thumb)

P Q R ,,, ___ \\/ ________ / \ _/\\ `^^^=__ \ //^||| || /\ //\ \/ // ||| \ ^/ // | | `´ |^ | | | (pointing hand) (V pointing down) (cross your fingers) (with middle finger) (pointing down 45°)

S T U ,,, ||| ____ __,_ _||| |||<\ ||||\ || /\ \^^^/ \^^^/ \ ^/ | | | | | | (clenched fist) (clenched fist) (two upright fingers) (with thumb on top) (with thumb between) (middle and index)

V W X ,, ,, ,, ,, ,, \\ // \\ || // _ __\\// \\||// __|| ||| / | /\ |||/\ \^^ / \ ^/ \^^^/ | | | | | | (Victory sign) (form a W) (bent index finger)

Y Z ,, ,, \\ || ___ \\___ __|| / ||||\___ |||/\ / \^^^/^^´ \^^^/ /__\ | | | | / (make a Y) (pointing finger) (move as Z)

I know my ASCII art is horrible, but I hope it gets the point accross.