postinst is in notify-osd 0.9.35+16.04.20160415-0ubuntu1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 | #!/bin/sh
set -e
case "$1" in
  configure)
   	killall alsdorf notification-daemon notify-osd 2>/dev/null || true
	 ;;
esac
 |