How do aircraft discern that an ACARS message is being sent to them? This may be a simple question, but how do airplanes know which ACARS messages are meant for them from the ground? I'm not sure how physically close planes would have to be in order for that to be an issue. Do they simply receive all ACARS transmissions in the area and the CMU checks for this information in the header and continues to route it if it has the proper header? I'm assuming the VHF doesn't perform any checks since the data is still an RF signal at that point.
A typical ACARS VHF transmission. 

Mode A 

Aircraft B-18722 

Ack NAK 

Block id 2 

Flight CI5118 &lt;&lt;&lt; looks like an identifier the receiver can filter on 

Label B9 

Msg No. L05A 

Message /KLAX.TI2/024KLAXA91A1 

https://en.wikipedia.org/wiki/ACARS