Obstruction Mechanics

[frozenrope22]

Hard ground ball between F5 and F6. R2 is advancing to 3B. F5 is moving to 3B as there might be a play. R2 and F5 get to the bag at the same time and there is contact. R2 rounds base and starts toward home. F7 comes up throwing and coach screams back. No play at third. Coach starts screaming "thats interference" and BU follows with "that is interference" and waves runner to home.
Aside from the fact that it should be obstruction, is there an umpires signal that indicates obstruction while the play is occurring? The BU had clear view of the play but didn't make any indication of a call until after the play completed and coach started screaming. 15U travel ball playing FED rules.