When you have found enough information about a stash it will be shown on your map - both the map in the PDA and in the minimap (if you're close enough). Once you find and loot a stash the icon will disappear. You can find information about the same stash several times - if you do, the contents of the stash will be multiplied by the number of times you've found the information; say, for example, you've found a stash with a medkit and 5 bandages in it. If you have found information about that stash three times, the actual content will be 3 medkits and 15 bandages. If you have found information about a stash more than once, without looting it in the meantime, the icon will not disappar from the map once you do pick up the items - I reckon this is a bug. You can remove the icon yourself by putting something into the stash and then taking it again; this should clear the stash marker off your map.