Problem
The manual says that level 50 Weaponsmiths "automatically know the damage caused by unidentified melee weapons", but it's also displayed for missile weapons, shields(!) and some missiles. Examples:
* "sling (+0, 1d2)"
* "heap of 2 tower shields {mithril} (-2, 1d5+2)"
* "bundle of 2 sling bullets {iron} (-2, 1d4)", "bundle of 3 black javelins {iron} (+1, 2d3)"

This only happens when those items are unidentified.

How to reproduce it
Become a level 50 Weaponsmith, then acquire unidentified missile weapons, shields or missiles.

Notes
Melee damage of shields, that's a nice joke :)