Thanks to eddypeck.
A aftermarket add on produced by a company called Metaplast. Popular in the 80's and as with most things retro, they're making a come back. Whilst you may have removed it and thrown it away in the 90's people are willing to pay silly good* for these now.
(http://farm7.static.flickr.com/6063/6121620234_0d66084f42_z.jpg)
* at time of writing the value tends to be around £100-200 for one of these. Recently a batch of NOS materialised, still in the original blister packagin and they were changing hands for £180 on eBay.
(http://i1117.photobucket.com/albums/k596/Jetta_GTD/VWVortex/886f5d3e.jpg)
See also the Kamei (http://www.vwgolfmk2.co.uk/forum/viewtopic.php?f=147&t=46858) and Lampa versions.