Thanks everyone for the discussion here. We used just a paint scraper for the letters and it worked fine...and then we noticed the reflective tape wrapped all the way around
=more tedious but necessary work
I kind of like that kind though. Definitely wanted that off so we attempted it with just a paint scraper, no go. Then moved to the sander, took a long time. Came on to the forum and within minutes I had my conclusion, Use my stinking heat gun I just ordered on Amazon for $20 for heating up steel before placing over removed windows, and for a didgeridoo project ;) So from all of the posts in a nutshell:
Paint scraper & Heat gun..if that doesn't work go to diesel/paint thinner...then sand the rough spots.
We did take some paint off with the the paint scraper and heat gun while removing letters/reflective tape/school bus stickers on rear and front, but I planned on sanding it and then covering with Corroseal to convert/prime any and all rust. Eventually we will wash and paint it.
Do you all recommend using paint thinner all over it or just using primer before painting the bus? I have seen both comments but not sure which is preferred and why. Thanks all for the awesome advice!