Your operating limitations will spell out how to identify yourself when calling a tower.  Some pilots seem to be in the habit of always saying "Experimental Such-and-Such"--probably the most conservative method--, others (like me) try to ID themselves as experimental on the first call to a tower.  I think I accomplish it most of the time, but not aways.  Realistically, most towers seem to recognize experimentals, which I believe is the whole point.  But there are production and AB Lancairs so ya can't be too careful I guess. See also AIM 4-2-4 Example 2.