It's no secret digital signage to this point has been a child amid grown-up media outlets. But a couple of signs have emerged that indicate this new medium may be reaching -if not maturity- at least adolescence.

While its boosters have long proselytized the medium as a powerful complement to other in-store promotional techniques and messaging, digital signage in the retail environment has remained "well poised," "an emerging voice," and other euphemisms for not mainstream.

That's easy to understand, based on the timing of its arrival on the communications scene. A recent Self Service article reporting on the "Building Your Digital Signage Business" conference in Chicago last month, quotes CAP Ventures analyst Norman McLeod as saying that reasons beyond the control of the digital signage industry have held back its growth.

The article, by Bryan Harris, quotes McLeod as saying the 2000 bust of dot com companies sucked venture capital from the market. Then, "we saw the biggest decrease in advertising since they started tracking it," he's quoted in the article as saying, in 2002. Only in 2005, did the market fully rebound.

However, with that rebound have come a couple of signs that in-store and out-of-store digital signage may be hitting its stride. In Britain, the Screen Association has published the first-ever directory of UK-based digital signage networks that accept advertising from third parties, according to a report from Clickpress.com. The directory, "The Screen UK Advertising Networks Directory," provides a full index of 62 such networks with details about the networks and contacts at each.

Publication of the directory indicates that diffuse digital signage networks -at least in the UK- may be congealing into a definable market that advertisers, advertising agencies and marketing professionals can quantify, measure and ultimately specify in their media plans. That's a big step for digital signage on its path to reaching maturity.

In the United States, a similar development indicates digital signage may be entering adolescence. Clear Channel Outdoor, one of the leaders in the outdoor advertising market, announced last month that it was expanding its digital signage network with several new installations in Tampa, FL, and Milwaukee, WI.

Reporting on the move for MediaPost.com, author Erik Sass quotes company CEO of Clear Channel Outdoors Paul Meyer as saying the move will help Clear Channel attain its 2006 goal of deploying digital signage in four to six markets.

As with conventional billboards, the LED signs, which measure 14ft by 48ft, will be positioned near heavily traveled roads. However, use of digital signage technology will allow Clear Channel to "day part" advertising to better meet the advertising needs of its clients and potentially charge a premium. As with news of the UK directory of digital signage networks, the latest announcement from Clear Channel demonstrates the congealing of the digital signage market into a medium advertisers can easily grasp. One can imagine national brand television advertisers supplementing their brand and product commercials on such giant electronic billboards. That opportunity will only grow as Clear Channel Outdoors and others build their inventory of outdoor digital signs across America.

What appears to be happening in the digital signage market are the first signs of an amalgamation of individual signs and networks into something that more resembles a definable medium than a scattershot straying of public venues and retail shops with unrelated networks and signs.

Market researchers frequently set about measuring the strength of the digital signage market in terms of forecasts, such as researcher iSuppli's recent projection of a $12 billion dollar value by 2010, its true health may better be predicted with the formation of viable advertising markets that exploit these sorts of digital signage networks.

While no one would argue that these networks trumpet the arrival of a fully mature medium, such developments indicate digital signage is reaching adolescence.