What is the difference between l and d and (+) and (-) sign in compounds?

small d and l are (+)clockwise and (-)anticlockwise respectively captital D and L as given below .

but there is a compound.... L (+) alanine which is dextrorotatory.

symbol 'd' or (+) is used for dexterorotatory optical isomer whereas (-) or 'l' is used to represent laeveorotatory optical isomer....a (+) optical isomer rotates plane polarised...