When using the deleted search operator, it would be nice to see an indication that it's definitely being used in the search, as is done for other search operators in the query description that appears on the right:
This would make it easier to see at a glance that I've formed the query correctly.
I noticed this after seeing a deleted answer from a destroyed user; when I tried to use search to review any other posts they had left, I didn't get any results, which seemed weird. My first instinct was that I must not have used the search function correctly and I spend a minute troubleshooting the query before realizing that the query was fine and finding the explanation on MSE.
