I think instruments associated with a single ethnicity should not count, because virtually all such instruments will be considered political in cases of ethnic conflicts. As we all know, the referendum in Turkey has an ethnic aspect, largely fueled by government propaganda.

The electric guitar is more to the point, but it stands as a symbol for rock music. Similarly, the saxophone is often seen as iconic for Jazz and thus for African-American culture - although invented by a Belgian.

The most "political" instrument I know of is an instrument called Martinstrompete or Schalmei, which in Germany of the earlier 20th century stood for socialism. The criteria were: 1. loud, 2. very easy to learn and play, 3. not permitting any sophisticated - and thus bourgeois - music. The Nazi youth activists, proletarians as well, chose bugles, and were very ambitious in terms of technical mastery (- not of musical sophistication, of course). The Nazis scored in this contest. -

Brexiters cannot have a symbolic instrument because they do not have a sufficiently homogeneous cultural image. What united the voters for Brexit seems to be that they wanted to get rid of Cameron. That was a success, at least.

As for Trump supporters, I tend to associate them with Country music, but this is certainly not the full picture (- even if we disregard the brave attempts at "liberal" Country music).