Slogan on the side of a DHL truck in Palo Alto:
DHL — YOUR SPECIALISTS IN INTERNATIONAL SINCE 1969
The adjective international is serving as a noun here, conveying something like ‘international shipping’ or ‘international mail’ or ‘international delivery’. Informally, this is “nouning by truncation”, but the implicit noun head isn’t uniquely identifiable.
Two pieces of background here: on “nouning by truncation” and on the DHL company and its slogans.