I have read about distinguishing them using osmotic experiments in books and here as well. But is there any thing common (on a biochemistry level) from which I can tell if a vacuole is contractile or non contractile irrespective of the organism taken and only by observing?
Contractile vacoules are usually surrounded by distinguishing structures
The contractile vacuole has several structures attached to it in most cells, such as membrane folds, tubules, water tracts and small vesicles. These structures have been termed the spongiome; the contractile vacuole together with the spongiome is sometimes called the "contractile vacuole complex (CVC). The spongiome serves several functions in water transport into the contractile vacuole and in localization and docking of the contractile vacuole within the cell.
This type of arrangement is not common in non-contractile vacuoles like gas, sap or food vacuoles.