class ActiveSupport::TimeZone

zone.formatted_offset(false) # => "-0600"
zone.formatted_offset # => "-06:00"
zone = ActiveSupport::TimeZone['Central Time (US & Canada)']

string if the time zone is already UTC.
Returns a formatted string of the offset from UTC, or an alternative

def formatted_offset(colon = true, alternate_utc_string = nil)
  utc_offset == 0 && alternate_utc_string || self.class.seconds_to_utc_offset(utc_offset, colon)
end