Conservation Listing

Buildings and structures which receive some degree of protection through local, regional and national laws, can be tagged in a variety of ways. In many countries a legal inventory of such man-made structures will be maintained at a regional or national level.

This page suggests use of conservation_listing=*, with values of grade_I, grade_II and grade_II* in the United Kingdom.

Alternatives already mentioned on the wiki are:

• use of designation=*. This is a generic tag designed for assigning a precise legal or organisational status within a specific jurisdiction or organisation, where the general tagging schema may not reflect details at that level. This has mainly been used to clarify status of public rights of way in England and Wales. It has been used for listed buildings in the UK (under 10 uses on tagwatch).
• use of preserved=yes, in association with historic=*.

Important

listed_status=* is far more widely used for listed buildings it seems. According to Taginfo there are around 4,000 uses of "listed_status=Grade[I/II/II*]" and only 5 uses of "conservation_status=*".