There are a number of different manufacturers who make essentially the same gun. JG, Cyma and Classic army are all clones of the TM gun. ICS is very similar but has some proprietary parts and sometimes a split gearbox. SRC are the same but the magwell dimensions are slightly different so it will need different mags. G&G MP5's will have blowback.
If there are no identifying markings, try different mags in it, if they all work then it is not SRC, if they all work but some brands don't feed as well as others it may be ICS.
Why does it matter? If its for the purposes of buying parts, it doesn't matter as they all take the same parts.