I notice players talk about SX hero from SX1 , SX5 etc. Unlike the S1, S2, S3 and S4 heroes which..

I notice players talk about SX hero from SX1 , SX5 etc. Unlike the S1, S2, S3 and S4 heroes which identify clearly where it come from. But how do we see or tell Avalanche is X6 hero , as the game just indicate X hero. There are no number display on X. How do we know which X hero is from which Season?