Recently I've been working toward digital urban sketching on a regular basis including creating classic car digital watercolor sketches at local car shows. I'm hopeful that I can pass the sketches on to interested owners of the cars during the show.
I've been using the Procreate app for iPad on my 12.9" iPad Pro second generation with some very nice watercolor brushes that I've received through my premium Skillshare account. I'm still working on my technique, but the process is that I make a blue line or pencil sketch in Procreate with direct observation, finishing the sketch later at home with color, using a photo reference.
I've been able to send a finished jpg file to interested owners via email. I've had business cards printed up to hand out with my information, and I write the owners email directly on the sketch layer in Procreate, since that layer won't show up in the finished file.