Q. Can one use or even keep a cheap common plastic pen left abandoned in a Yeshiva or shul?
A. Horav Shlomo Miller’s Shlit’a opinion is that, if it looks abandoned and does not have any specific siman or identifying mark on it, in need one may use it.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller, Horav Dovid Pam and Horav Aharon Miller Shlit’a.