To signalize points on the minimap for the player, you can ping it via PingMinimap/PingMinimapEx jass functions. However, you cannot set the ping's duration to infinite and handle them as deletable objects natively. So my first idea is to create a custom object type that holds x/y coordinates and periodically pings that spot until deactivated/destroyed. If you had multiple pings at the same time, of course, you would want to distinguish them. That is why my second suggestion features pings in random different colors. In open RPGs, you are often able to arbitrarily choose a big amount of quests, so marking them by a specified, fixed color is inconvenient and may lead to overlapping. Randoming the color would select and remove it out of a preset pool and even if you exhaust it ingame because whatever reason, it may still automatically create new colors. To tell the player of which meaning a certain ping is, ask its color and embed it into a description etc. This is just a player-informing design that I have not seen until now in Wc3 but I think is simple and intuitive.