the first universal postal system was started in the United Kingdom with its Penny Black, the postmark used red ink for contrast. This was not successful, and the stamp was changed to non-black colours so that the postmark could use black ink. The majority of postmarks today are in black, with red (particularly in the United States with local post offices' handstamps) following, though sometimes they are in other colours. This is particularly true in the case of pictorial postmarks if the colour in question has some connection to the commemoration. Digital postmarks In 2004 the United States Postal Service announced plans to introduce first day digital colour postmarks to be used to cancel some first day covers for commemorative stamps in 2005 and this practice continued and was ongoing as of 2015. Postmark advertisement Singapore Post offers a "postmark advertising" service which, strictly speaking, applies to the "killer" rather than the postmark. Hungarian Post Co., Ltd. offers a similar service. Unusual postmark techniques There have apparently been some postmarks producing a stereoscopic or "3D" effect where a special viewer is required. They are considered more as a novelty than as a practical postmark. The local post Hawai'i Post had a rubber-stamp postmark, parts of which were hand-painted. At Hideaway Island, Vanuatu, the Underwater Post Office has an embossed postmark. Valuation of cancellations The study of postmarks is a specialized branch of philately called marcophily. It may bring added value to the stamps by their historical significance. Other parameters are the rarity and the attractiveness. In particular, the stamps issued by the Empire of Austria during the 1850–1867 period (the 5 issues before the Austro-Hungarian compromise of 1867), are collected for their variety and beauty. More details can be found in Valuation of cancellations of the Austrian Empire. A special or rare postmark can substantially add to the value of a stamp. Also, in addition to everyday postmarks there are postmarks indicating the first day of issue of a particular stamp and pictorial cancellations commemorating local events, anniversaries, and the like' and slogan postmarks which advertise an event or pass information to the public. (There has been a recent change to the term "pictorial postmarks" rather than "pictorial cancellations" by the USPS.) There are some examples of "faked covers" produced by philatelic forgers, most usually to increase their value, in which the postmark has been altered in some way; for