RTD had a rather interesting way of marketing the subscription services, no doubt due to the higher-priced "premium" nature of the service (the line records document the agency's diligence in assigning the cleanest, best-running buses to the subscription lines, even issuing a mandate during summer months that a bus was to be replaced if, when started at the division yard, its air conditioning failed to operate). In marketing the service, the above-average service was often made to look as little like public transportation as possible; as an example, here is a copy of a 1973 brochure for the ARCO-sponsored Line 505, issued shortly after its beginning operation:
Brochure Front Cover
Brochure Back Cover
Inside of Brochure
Note the presence of a "bus stewardess" (complete with hot pants and go-go boots) serving refreshments to the passengers!
The marketing efforts -- at least for this line -- appear to have been successful, as Line 505 lasted almost ten years before being replaced by more conventional express service in 1983. The ARCO-sponsored lines held the longevity records for subscription service, having been the first created and the last remaining.