Go to halfrauds and buy some Autoglym Super Resin Polish. Apply with a Microfibre applicator and remove with a microfibre cloth, couldnt be easier IMO such an easy product to use. Sounds like your paintwork has marring or light scratch marks....I assume he used his finger to write in the dirt? SRP will hide the marring, actually itll probably remove it, and mask light swirling. Itll also look a little better too. Use a wax on top of it if you want to "seal" in your work and make it last longer.
Try it on the bonnet first if youre worried about ease of use that way youve only got a single pannel to work on if you dont like it.
If not pay for a detailer to do it.