Python: assign custom tag to vertices Is it possible to associate a custom tag with each vertex?

I would like to be able to number them... 

I have an export script that dumps 6000 vertices to file, I then run a simulation that generates an array for each vertex.  

But I would like to be able to give each vertex a unique ID as it is written to file, so that I can select a dozen vertices in blender, and export a list of IDs (and then process the array for each)

How can I do this?

LINK: http://blenderartists.org/forum/showthread.php?318031-Property-for-each-individual-face
It is possible to tag vertices with the bmesh module:

bm = bmesh.from_edit_mesh(obj.data)
#or
bm = bmesh.new()
bm.from_mesh(obj.data)

#create custom data layers
my_id = bm.verts.layers.int.new('id')

#get the custom data layer by its name
my_id = bm.verts.layers.int['id']

#access
bm.verts[0][my_id] = 42

#apply the changes
bmesh.update_edit_mesh(obj.data)
#or
bm.to_mesh(obj.data)