Google seems to have a growing interest in melding location with social media. This has played out in lots of ways including last week’s launch of its Latitude mobile social product. The latest move comes with today’s integration of a location signature integrated into Gmail.

Users who turn on this function will have an auto-signature note that identifies their location (i.e., “sent from Mystic, CT”). Location will be determined by IP address but more precise location can be determined by Wi-Fi positioning, which requires downloading Google Gears.

This is conceptually similar to Yahoo’s Fire Eagle, which positions itself as a switchboard to provide location information to publisher partners that can use the location for more relevant user experiences.

As we’ve written, Wi-Fi positioning will soon be more omnipresent when it’s integrated into the browser. In the meantime, the extra step required to actively download tools (such as Google Gears or Skyhook Wireless’ Loki) will be a big adoption barrier to location-aware Web apps.

The location awareness already built into mobile devices, conversely, makes adoption more passive and frictionless than on the desktop. We’re likewise seeing a growing use case at the three-way intersection of mobile, social and local: Finding things to do, see or buy in the context of where my friends are and what they’re doing.

That’s where Latitude comes in, and the new Gmail location feature could somehow tie into it in the future. Until then, it’s more of a general correlation that points to Google’s interest in having location be an input in the factor that has defined the company’s products since the beginning: relevance (and revenue).

Social + mobile + local will be part of the discussion in the Mobile SuperForum at next month’s Marketplaces conference, where uLocate CEO Walt Doyle will be on hand to talk about what his company has done with the WHERE and Buddy Beacon mobile applications. Hope to see you there.