Some of the most obvious tribal markers in cultural evolution are uniforms. Sports teams, military, religions, companies and other organizations all use uniforms as means of signalling shared memes. These can then act as targets of altruism via cultural kin selection.
If we classify uniforms as examples of primary tribal markers, then we can also recognise the existence of various secondary tribal markers. For example, badges, bumper stickers and tatoos all function as tribal markers that don't dominate the appearance of individuals. Using secondary tribal markers it is possible to simultaneously signal affiliation with multiple organizations.
Another way to classify tribal markers is whether they are voluntary or not. Most secondary tribal markers are voluntary. However there are many cases where workers are made to wear uniforms where they would not choose to do so - unless they were being paid to do so. Among incarcerated prisoners, uniforms are not voluntary in any way at all. Things like language and money are interesting corner cases. They are often dictated by the rest of the society - giving the individual few realistic options. These also serve other functions besides signalling tribe membership, though.
Another interesting case is markers that denigrate out-groups. Normally secondary tribal markers promote in-group members. In biological systems, competitors are not normally worth wasting resources on. However, the is the phenomenon of local competition. If rivals are few in number - for example because they are nearby - then it is sometimes worth attacking them. In the cultural realm, we see this with negative advertising targeting political rivals. In politics, there are often only a few viable competitors - and it is possible to profit by attacking them. Often such attacks are performed semi-anonymously - and so individuals don't often associate themselves with such attacks. It is observed sometimes, though. Check the bumper stickers (below) for some examples saying: "JAIL BUSH", "TOO OLD", "SCUM", "YUK!" "JERK", "SCHMUCK", "JACKASS", "SHAME" and "IDIOT".
Tribal signalling is an example of memes harnessing our genetic tendencies. Animals often favour their own kin. Tribal markers create cultural kin - kin that share memes rather than genes. A superficial similarity of appearance is created - and this then triggers animal kin-selection circuitry, which fosters cooperation, which in turn helps the memes associated with the tribal markers to spread.
Tribalism has been studied by anthropologists before the advent of cultural kin selection - but they have generally lacked a proper theoretical framework with which to interpret it. While this situation is obviously deplorable, at least there's a lot of data with which to test more modern theories.