(S) = Simplex, same frequency for tx and rx and no (+) or (-) on your display meaning no offset.



If you can not hear the other stations using that same simplex station you are using that only means
you are out of range of that other station because a
simplex station is not repeating what you say locally.
The RF is traveling from that other station to you and not being repeated through a repeater.



But you will hear the other stations calling in through the IRLP because that is coming out of the
simplex radio to which you are tuned.