When the square root sign is put over an expression, when is it expected to put the +/- results of the evaluation of that expression?

I have made the following assumptions, please let me know if they are correct:

if there is no plus or minus in front of a square root then it is implied that only the positive root is wanted

if there is a negative sign in front of the square root then it is implied that the negative root is wanted

if there is no plus or minus in front of a square root but the solutions show you a positive and negative answer then