@Nutbolt
Just put a TriggerZone in front of the door and attach this script to it:
;Artificial Intelligence Script
;Header
desc = Message in Zone
;Triggers
:state=0:hudreset,hudx=50,hudy=90,hudimagefine=texturebank\user\YOURMESSAGE.tga,hudname=Message01,hudhide=1,hudmake=display,state=1
:state=1,plrwithinzone=1:state=2,sound=$0,hudshow=Message01
:state=2,plrusingaction=1:hudfadeout=Message01,state=3
:state=2,plrwithinzone=0:hudfadeout=Message01,state=3
;End of Script
Replace YOURMESSAGE.tga with the name of your message file.
Save your message picture in the texturebank\user folder.
The message will come up when you enter the zone and fade out if you press enter or leave the zone.