I would like to use a consumer grade inkjet printer (entry to mid grade) to print on self-adhesive vinyl. These labels would be for outside use, so the ink could not simply sit on the surface of the vinyl. The labels do not have to be resistant for months, but the colors/ink should obviously not wash away and be permanent. I would like to do this without using a laminate so I am guessing that the printing technique would have to embed the ink below the surface (?)
What would be the best way to accomplish this?
Vinyl printed with an inkjet printer like a Mimaki or Roland should never be used in an exterior environment without a proper laminate. If this sticker is going to be used temporarily, no more than a few weeks, you can get by with this.
Now what you really should be looking for is a sign company that offers "thermal transfer" digital printing. The best way to understand what this does is it technically burns ink on top of vinyl and can be cut to size. Laminates are not required but they are typically offered for protection over scuffing. This form of printing is used with warning labels, bumper stickers, and the like.
If you are looking for a DIY option there are some low end printers you can buy.
Now also be aware I am taking from your post you want to do a reverse, aka, reflective print, because you stated you don't want it to be scratched. Now due to this statement, regular inkjet digital printing is terrible. Without it being laminated you can literally run your finger nail across the print and it "could" come off (of course this also involves: print time, humidity, curing, etc, etc.). If you are really concerned about the print you could always do a reversed print on clear vinyl but that would depend on the substrate the vinyl is to be applied to.