<div style="float: right;">
{xen:datetime $serverTime, 'absolute'} UTC
</div>
But as I said before, the time is not in UTC. It uses the timezone of the current logged in user. You will find that if you change your timezone the reported time will change.
Unfortunately I don't know of any template function or other method to output a specific time zone. The time zone is available in the visitor array, but only as a string (e.g. ["timezone"] => string(19) "America/Los_Angeles") which can't be used for an offset calculation.