Hi Kay,
Eddie has give a very nice example of hand signals. I don't know if there's any "commonly used signals" in Scotland, but in Switzerland, most Skips / teams will use their own signals.
For example, I normally indicate the length of a draw weight by pointing to it's final resting position. A guard will be indicated the same way, possibly with the help of using fingers (because my team has divided the sheet in 11 different areas and given them names/numbers. For example 1-3 are our guard weights with 1 being just over the hogline and 3 being a thight guard just short of the house).
For take-out weights, we use this:
moving the broom horizontally across the backline indicates a backline-weight, e.g. a shot that just rolls out of play on it's own.
tapping the hack with the broom indicates a hack-weight take-out
placing your flat hand on your stomach indicates a soft-take-out (named "10" because it ideally takes between 10 - 10.5 seconds to pass from hog to hog).
our standard take-out "9" is a flat hand placed on your chest and our heavy weight ("8") is your arm across the chest and touching the outside of your other upper arm.
Quite a bit to take in at first, but actually pretty easy once you get the hang of it.
But as mentioned earlier on, every skip/team will have a different system (both for indicating weight to be played and for giving feedback on the actual weight of the shot while in motion) and you'll have to ask your respective skip what his system is.
By the way Eddie, did you look for this website?:
http://www.curlingbasics.com/