The first nave window

This window is slightly obscured by a loudspeaker on the right side.

The handshake, or grip, is a sign of friendship, unity, oneness of purpose and allegiance or devotion to a joint cause. The right hand in particular is an emblem of friendship, and the window detail shows two right hands.

The stole that is wrapped around the two hands is a priestly garment that symbolizes the bonds and fetters with which Jesus was bound during his Passion; it is usually ornamented with crosses, as in this case. The stole and handshake together particularly emphasise the bond of friendship.

The letters I, H, and S are the first three letters of the Greek name for Jesus (see HERE for an explanation).