This symbol is part of the mushaf, but not of the Quran. As later during the time of the Omayyad dynasty some scholars have done efforts to divide the Quran to ahzab أحزاب (plural of hizb) -mostly under the pressure of al-Hajjaj ibn Yusuf at-Taqafi- the idea apparently was either to have 60 hizbs حزب because the Quran should be completed at least each two months or 30 juz' جزء (part, plural ajza' أجزاء) to complete it each month (see for example this post). These parts have been also divided into quarters (arba' أرباع singular rubu' ربع), half/halves (nisf نصف/anssaf أنصاف) and eigth (athmaan أثمان singular thumun ثمن) so the sign or symbole you see is referring to one of these division parts: it marks the end of one of these divisions. In most actual mushafs a hizb is divided into quarters so a hizb constitutes of 4 quarters and the symbol would therefore be the mark of the end of such a quarter.
Note that the words hizb حزب and juz' جزء are quoted in ahadith like here in sahih Muslim and in the Quran, but the meaning or use in the Quran is refering to jamaa', community, camp or party.
Also note that the sahaba (according this Arabic source) themselves used to complete the quran each 7 days so the understanding of hizb differs a lot from the one we now find printed in the Quran. This is logical as the division made by those scholars is dividing a surah and therefore day may divide a meaning or let you stop at a point where the story continues. So this was a kind of muhdath act and as said it is definitely not part of the Quran and not a divine division, but a man made one.
Also note that these divisions may help to memorize the Quran, and are mostly used for this purpose an other option is to memorize it by pages therefore people who memorize always advise to learn and read from the same mushaf copy, as pages could start with different words and verses in different mushafs, even if in modern times this would rarely be the case.