Hide my updates from friend's Steam Activity pages?
Back in August 2012, Valve rolled out some community updates, including the "Friend Activity" page, which amongst other things can list which achievements your friends have acquired, which games they've purchased, and community content they've submitted:
Is there a method to hide my activity from appearing on my friends' "Friend Activity" pages?
It's not an ideal solution, but you can hide your public activity by setting your profile to private. Note that your previously posted activity may remain in your friends' feeds. (Thanks to OP for testing this.)