the "red_nose" tag states in the wiki :
"A red ball that can be fitted over the nose. Can either refer to the Christmas tale Rudolph the Red-Nosed Reindeer, or to clowns who wear them"
it is used as stated in the wiki, like post http://danbooru.donmai.us/posts/1326465 but also used as it means - a read nose - like http://danbooru.donmai.us/posts/2182571
the tag "clown_nose" has no wiki page and it would fit the sentence above, but is not used with the red_nose tag (only 1 image shares both tags)
red_nose tag is used as it means - a red nose - maybe merch the tags together? the meaning as in red nose, clown nose, nose from a cold, drunk nose (last two, if the artists chooses to draw it that way) still has the same meaning and is easy to search.