The tag is present in Lintian version 2.109.24. That is the most recent version we know about.
This package appears to build both -dbg and -dbgsym variants of a package. Only one package should contain the debug symbols
Usually the -dbg should be dropped in favour of the -dbgsym. However, in some cases (e.g. Python modules) the -dbg contains more than just the debug symbols. In these cases the -dbgsym should not be built.