Having validation fail if the input is empty but required is sufficient, but it does seem a little off-putting since there is no visual indication in the UI that the element is, in fact, required.
Ideas for a 'required' indicator:
Arc-style: parenthetical '(required)' next to the label
Red asterisk in label
Image indicator in the UI element itself
As suggested by this SO post (http://stackoverflow.com/a/1861088/299084), perhaps slightly smaller, parenthetical (required) next to the input title would be sufficient.
Having validation fail if the input is empty but required is sufficient, but it does seem a little off-putting since there is no visual indication in the UI that the element is, in fact, required.
Ideas for a 'required' indicator: Arc-style: parenthetical '(required)' next to the label Red asterisk in label Image indicator in the UI element itself
As suggested by this SO post (http://stackoverflow.com/a/1861088/299084), perhaps slightly smaller, parenthetical (required) next to the input title would be sufficient.