Do you know what the sign is for...

During our quest to get Miles to communicate we've been using quite a bit of sign language.
The results have been amazing. He usually starts telling me he wants something by having a meltdown. If I start making guesses, he gets mad because I don't guess what he wants.
After a few minutes of meltdown mode, I will ask him to TELL Me what he wants and he'll do the sign for 'eat' or 'more' or 'milk'.
Logan thinks this is great.
We had the one and only Mom Underground over with 'big G' and 'little G' last week. Logan was completely amazed to hear 'little G' say with such clarity, "Mama".
"HEY! He said MAMA!!!!" like it was thee coolest thing to hear a little kid say a word.
All day long he talked about how 'little G' can say this and that.
I try to convince him that soon enough Miles will be able to say words, but Logan has his doubts.
So when we started teaching Miles to sign, you can only imagine the excitement that Logan had. Miles communicates in other ways that crying so loud that Logan can't hear the TV. Yeah for that! :)
Apparently we may have gotten a little too excited for Miles because Logan now thinks he knows the signs to everything.
In the car, when he hears the radio, his fingers and hands are doing all sorts of movements.
"What'cha doing kiddo?"
"I'm signing the song!"

When he wants more of something, he'll make up the sign.
"Do you want to see how you say, 'I want more turkey sandwich'?" he says as he shows me his hands and fingers flailing around.
"Awesome! Show your Dad!" I say as I watch him show Dave something completely different.

Hopefully Miles will decide that he can communicate by speech, but heck, we're doing pretty good making up signs along the way!
Although, I'd like to learn a few more that would make life easier.
*Water
*Tired
*outside
*brother

Can anyone help?