You can cause the text to change to uppercase when you exit the field--may not be exactly what you want...
Use this auto-enter calculation on the field:
Upper ( Self )
Also clear the "do not replace existing value..." option.
I'm looking for something the user can Identify straight away, this only works aftrer leaving the current field.
With the OnObjectKeystroke Script trigger, you can process input to the field one key at a time. Such a script can map lower case input into upper if that's what you want it to do. The user will simply see their input appear as all caps if you get the script working correctly.