hi im a 16u softball player and for softball theres alomst no such thing as a uneversal sign for pitches they will most likely change as you go along.
so right now pick simple signes that the pitcher feel most comfterble with.

Signs are up to each coach/team. Often there are two signs: type of pitch, then location of pitch. Some have rotations of signs that change from game to game, or even mid game if they believe the other coach has picked them. Some keep the same signs, but throw 3-4 and the pitcher knows to take the first two or last two.

Check your catcher to make sure she hides her hand well and that she doesn't set up until her pitcher is in motion.

I agree with the others. There are no universal signs. Most teams I know have different signs. Most do give a sign for the pitch and the location. Some only give inside and outside as locations, others have more specific locations that they give.

It's really up to you how you want to do it and how simple or complicated you want it to be. I'm typically in favor of simple, especially at the younger age levels.

I remember in college (DI), the numbers flashed were the pitch (catcher would flash 3 numbers and the middle one was the live signal), then they'd just tap a knee for in or out - simple.

I know high school teams that have far more complicated signals!

Since you are coaching a younger rec team, keep it as simple as possible. Only give them as many pitch signals as they need. So if they can only throw two different pitches, minimize the signals to that for that pitcher. There's no reason for her to learn 10 signals when she only has two pitches. Pitchers need to stay as focused as possible and the signal giving isn't something you want hindering that.