Proper mechanics - FED obstruction

[rbmartin]

FED ruleset. 2 umpires. I am HP. Runner on 2nd, no outs. Batter hits cleanly to center, throw coming to F2 from F8. As ball is on flight, runner slides (no MC) and IMO is obstructed by F2, who then catches the throw and applies tag to runner before he touches plate. F2 then immediately throws to 2nd in an attempt to get BR advancing to 2nd. Tag is sucessful at 2nd.

My call is : obstruction, run counts.

My question is , exactly what should be my signals and verbalization for this call?