I'd suggest you using tsts utility from moreutils package.
Though its primary purpose is prepending output lines with a time stamp, it can use an arbitrary string along or instead of the timestamp
for line in {01..05}; do echo $line; done | ts "A string in front "
A string in front 01
A string in front 02
A string in front 03
A string in front 04
A string in front 05