Who owns the signs? And why won't they take them down?

I've noted a couple of signs in Northern Virginia that indicate the way to Dulles Airport.  One is on Route 50 in Arlington just past the Courthouse exit at the 10th St. exit.  The other is on Little River Turnpike between Braddock Road and Old Columbia Pike.

View Dulles Airport signs in a larger map

Here's what they look like:  

This is the sign on Route 50 in Arlington.

Here's its location.  You can see the 10th St. exit sign that is in the median.

Here's the one on Little River Turnpike.

The existence of these signs raises a number of questions:

• Who owns them?
• How long have they been there?
• Why are they still there?
• What purpose do they serve?

I suspect these signs date from before I-66 was built, since no one would take Route 50 to get to Dulles with I-66 available.  Also, neither of these--as far as I have noticed--has any follow on signs, so a traveler who noted the sign would never see another one to guide them on their way.  A single directional sign far from its destination without any more to assist the traveler is probably worse than no sign at all.

There may be more of these Dulles airport signs.  Have you seen any?  Where?

Taking a macro view, who is responsible for signage in general?  Once a sign is placed is it ever taken down?  I've seen signs in my neighborhood that have rusted so badly they can barely be read and that are completely outdated.  Signs like these are everywhere, and they just accumulate.

Perhaps every sign should have information on the back of it that tells who owns the sign and who is responsible for it, as well as contact information.  At least that way someone could try to follow up and notify the owner if it gets damaged or becomes obsolete.
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Steve Offutt, Arlington