The term "to have dibs on something" or "to call dibs on something" plays a recurring role in American film and television (e.g. How I Met Your Mother), so it gets exported a lot.
Wikipedia describes "dibs" as
[...] a common, "informal" convention to reserve or declare full or partial ownership of a community resource, such as a chair [...]
From the usages in the media I have seen, this convention also seems to contain some moral concept which is not described in dictionaries. For me, it looks like by calling dibs (or shotgun), the caller actually receives the (implicit, moral) right to that resource, and this typically goes undisputed by their rivals.
Can you confirm the existence of this concept? Is this something that varies between groups of people (or maybe between regions), or is there a concensus on how to respond to this?