Similar to dynmap, enable players to create markers using signs.

A player with the permission bluemap.signs can create a marker by placing a sign with the first line being [bluemap] and the following lines being the marker's label. When the sign is broken/destroyed the marker is also deleted.

Such a feature will not be added to bluemap itself, because it's a very server and implementation-specific feature, but:
Its totally possible for any developer to make an addon-plugin using BlueMaps API that adds this feature! :)