A couple of interesting things, here. First, “No Saving Space.” It rings odd, because in most circumstances, “Saving Space” is a good thing. When packing for vacation, you leave bulky items out of your suitcase to “save space.” Etc.
Note also the use of the word “forfeits.” Is that a widely-understood word? (I’m a professor, and I would be cautious using that word with, say, junior students. It seems like an upper-level bit of vocabulary.) I’m not sure I’ve ever seen that word on a public sign in North America.
Note finally that this is not a rule that anyone of the workers at the roller coaster is liable to enforce. It’s just a statement of…well, it’s an assertion of not just a rule, but a kind of moral truth. By doing X (leaving line) you cause something to happen (namely, you have caused yourself to lose a certain status, that of the legitimate owner of that place in line).