The symbols as they are printed on my keyboard matches what Wikipedia calls the Linux US layout[1], but I'm pretty sure I bought this in the Netherlands and an ordinary Logitech K200 will not have custom Linux prints on it, so I'm a bit confused. There also exists a Dutch layout with the same physical keys but a different keymap[2], so that's not it.
Trip down memory lane: until Vista, Windows in Dutch shipped with the Dutch and US keyboard layouts both enabled (US was the default) and ctrl+shift as switching hotkey. People would randomly get plusminus symbols when they tried to type a colon because they had accidentally switched to the Dutch layout, which was printed on exactly nobody's keyboard. It happened so often that people would just roll with it, and I think it was generally understood among the heavier computer users that plusminus was supposed to be a colon. Sometimes, someone would reply to such messages: "press ctrl+shift and try the colon again". That person was then thanked profusely. Those were the days.
[1] https://en.wikipedia.org/wiki/British_and_American_keyboards...
[2] https://nl.wikipedia.org/wiki/Toetsenbord_(computer)#/media/...