There are many ways to do this and many different levels of difficulty, but the easiest way to do something like this ...
Add an interceptor function to the field initialization method, which adds a question mark and uses qtip to display the message - this allows you to use all types of fields that inherit from the Field class for this function.
For instance:
Ext.intercept(Ext.form.Field.prototype, 'initComponent', function() {
var fl = this.fieldLabel, h = this.helpText;
if (h && h !== '' && fl) {
this.fieldLabel = fl+'<span style="color:green;" ext:qtip="'+h+'">?</span> ';
}
});
Then in each field definition you should have the helpText property:
{
fieldLabel: 'First Name',
helpText: 'This is your first name dummy!',
name: 'first',
allowBlank:false
}
This gives:

, , , , .
!