A location tag (sometimes called a geo tag) is a deliberate visible indicator on a post indicating the location that it is about, either directly in the post from its author, or sometimes as a reply to the post.
None for location tags in particular so far.
See location#IndieWeb_Examples for general IndieWeb Examples of location information in posts (some of these may be close enough to "location tags" to merit including/moving here).
(suggest location notification screenshot needed)
If you (as the author of the original post) accept the location tag notification (possibly another response?), then that shows up in location tagger's notifications as a "so-and-so accepted your location suggestion on her photo."
- (white location pin on pink background mini square icon) n minutes ago / about an hour ago etc.
(post with location tag screenshot needed)
Then the post itself shows the location as it would if the author had originally specified it themselves.
There is no indication that the location information came from a location tag post from someone else.
How to markup
The proposed location-of property could be used to markup a location tag reply post. See that page for more details of how that could work: