Purpose of stickers copying license plate number?

On every seemingly 'official' taxi and bus in Peru (including vans and minibuses that seem to be owned by local travel agencies) you see copies of the license plate numbers painted on the vehicles;
usually in the form of stickers but I have seen hand-painted signs on old taxis:
What purpose do these serve?
Some bureacratic proof of licensing, anti-theft measures, ...?
Do they mean anything for me as a traveler, i.e are they supposed to guarantee something?
Notes:
- Private individuals playing taxi don't have them
- I have seen two repair(?) service cars from private companies with these stickers as well
Best Answer
Most countries that require such do it a means of readily identifying a vehicle. No matter which door you get out you can see the taxi's license number. A lot of countries require the same info posted inside the cab.
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