Reference the advertisement according to the style for the source, i.e. an advertisement found in a journal, magazine or newspaper should be treated as much like an article from that source as possible.
Advertisement: print (magazine)
(The Wine Company, 2013)
The Wine Company. (2013, June 28). Discover our bestselling Marlborough Sauvignon [Advertisement]. Private Eye, 38.
Company name. (year, month, day of publication). Title of the advert (if there is one) or strapline or slogan [Advertisement].
Title of publication, Page number(s).
Audi. (2013, December 2). The new Audi Q5 [Television advertisment]. London: Channel 4.
Company name. (year, month, day of transmission). Title of the advert (if there is one) or strapline or slogan [Television advertisement]. City of origin, i.e. where the programme was produced: Name of television channel.