Can anyone identify this resistive component?

I believe they are Tyco/Raychem TRF600-150, high-voltage resettable fuses, rated for 250VDC nominal (600VAC interrupt rating) and 150mA nominal.

I found a Tyco/Raychem datasheet that seems to match general part package and specs. Excerpt from page 10 (note the minimum resistance of 6Ω in the datasheet, which matches your measurement):

Raychem went defunct in 1999, and were acquired by Tyco, so maybe they are now available under that brand name. If you search Ebay for "Raychem 600 150", you'll find various listings for parts that look exactly like yours.

One example, from this listing, claiming to sell "RAYCHEM PTC Resettable Fuse Radial Leads .16A/.32A 250V 3A NEW 5/PKG":

The bottom row on these says XS1G rather than your WN1U. This is probably a production series code, which differs from batch to batch.

Here is another listing, claiming to sell "( 25 PC. ) RAYCHEM/TYCO PTC TR600-150-2 RESETTABLE POLYSWITCH CIRCUIT PROTECTOR":

It's a 0.15A, 60VDC (600VAC interrupt rating) resettable PTC fuse.

An equivalent is here:

http://www.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_600r_datasheet.pdf.pdf

http://www.littelfuse.com/products/resettable-ptcs/telecom/600r.aspx