Any asset code ending with a ".S" represents an On-chain staked balance. For example, XTZ.S represents On-chain staked Tezos while XTZ are non-staked Tezos.

Any asset code ending with a ".M" represents an Opt-In Rewards balance. For example, BTC.M represents Opt-In Rewards Bitcoin while BTC are Bitcoin are not Opted-In.

Any asset code ending with a ".P" represents a Parachain balance. For example, DOT.P represents assets bonded to parachains. 

You may notice staked balances when looking over your Ledger History.