You can place contact information on the General tab of the System Properties which is displayed when you run the Control Panel System applet.
Create a 180 x 114 .BMP file as %SystemRoot%\System32\OEMLOGO.BMP (hopefully you will do a better job than I did).
Using a text editor, create a %SystemRoot%\System32\OEMINFO.INI:
Manufacturer= JSI Inc.
Model=Your Windows NT Resource
Line1=" Free support "
Line2="for our > $500"
The \[Support Information\] displays when you press the Support Information button. At my screen resolution (1152 x 882), I had no trouble fitting 16 lines of 55 characters, as the Figure shows, but your mileage will vary.
You do not need to logoff or restart as the information is read each time Control Panel starts.