Sign, Signal, Diagram, Phase Diagram
noun, する verb
A mutual diagram is one that's for everyone to see. It's a sign.
あいず
The reading is a combination of kun'yomi and on'yomi readings. That being said, both readings for both kanji are the readings you learned already, so you should be able to read this.
相図をしたら、スクワットを始めて下さい。
Start squatting on my signal.