For the marker you use at 3:48 youre probably better off getting a correction pen and just filling that up with ink. It will write on anything, is probably cheaper and the marker itself will make way better tags. Unless you really like "micro tags" I suppose.. I see later in the video you actually do exactly that.
unique stuff man, absolutely love it and you deserve an extra sub. though i'd hate to be in Berlin and seeing an ominous red eye staring me down ahahah