You need to create a background program in which you will check about the air pressure signal. To display on the interface panel you need IFPWPRINT function. You have to create on the interface panel a strings window.
For example:
.PROGRAM autostart.pc ()
;initialisations
IFPWPRINT 1,1,1,6,1=""
$msg1 = "Message 1:"
;main loop
loop:
IF SIG(-1006) THEN
.$msg1 = "No air pressure."
ELSE
.$msg1 = ""
END
IFPWPRINT 1,1,1,6,1=$msg1+.$msg1
TWAIT 0.1
GOTO loop
.END
The message will disappear when the signal is ON again, no need to have a reset button.