I've just make some smoke markers from traditional pipe cleaners. The bottom picture shows how I've twisted the pipe cleaners around each other, I then twisted another around the base of the arms. This was then supper glued onto a 1p coin to act as a base. I'm not sure about painting them yet, they look good as smoke markers as they stand I think, but as they are so cheep to produce I might have a go at using some grey primer spray paint on a couple and see how they turn out. As for scale, I think they should work with my 15mm and up to 28mm scale should be fine. They might be a bit over scale for 1/300 scale, but you could scale the size down a bit.
Graphic designer working in the Manchester, graduated in the mid 80’s pre Apple Mac. Twelve years working in advertising as a graphic designer in London, back home to Shropshire with the wife and daughter in the mid 90’s.