/usr/bin/urxvtcd is in rxvt-unicode 9.20-1+b1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
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#!/bin/sh urxvtc "$@" if [ $? -eq 2 ]; then urxvtd -q -f exec urxvtc "$@" fi