diff --git a/APCO25.md b/APCO25.md
index eb3d850..e1d34be 100644
--- a/APCO25.md
+++ b/APCO25.md
@@ -64,6 +64,11 @@ configuration window.
 When aliasing talkgroups and radio addresses, ensure you include the full 4 or 6
 character talkgroup or address with leading zeros.
 
+Add these trunking system unit ID values to your alias list:
+*FFFFFD* = (Trunking) System Controller.  
+*FFFFFE* = Registration Controller
+*FFFFFF* = All Call 
+
 ## Modulation ##
 
 Choose either C4FM or LSM Simulcast (CQPSK) modulation in the channel configuration