Since Dark And Darker Gold is a game that is still in the process of development, so a lot of the details and mechanics, overall will change over time and nothing is easily accessible about all its components. However, here's the information players have gathered concerning blue Headstones as well as Escape Portals to date from the alphas that have multiple versions:

The sound cue for Blue Headstones is a noise like the sound of rumbling stones as well as an opening of an ancient stone gates. This is the sound that the stone is rising up from the ground. But be aware that having three of these sounds being heard at the same time is an indication of Red Headstone trio spawning, that is the portal spawners that lead teams further into the depths of the dungeon.

Exit Portals/Headstones typically appear within the security of the circle. However, should they ever appear outside of the circle however, they're very near. It's not clear the exact time to spawn of Blue Headstones yet, but they appear early. The spawning process isn't instantaneous, however, within about 8 minutes, the Event Feed announcement of exit Portals that are spawning will begin to show on the upper right.

After the portal has been spawned and is open, it remains open until it is used, which means players can access it, complete some last-minute looting and then leave without having to interact with the headstone once more. In the second beta at the very least, Blue Headstones tend to spawn in groups close to each other. Therefore, if a group of three finds only one Headstone is best to explore the surroundings instead of arguing about who will be the first to get exfiltrated.

Sound is a major factor because it is the case with almost every system that is Dark and Darker. The players who are looking for Blue Headstones need to be continuously listening for audio signals for footsteps mixed with the noise of the Headstone and the sounds of Wizard spells that are charged or the general sound the Cheap DAD Gold Escape Portal makes.