Or fouling point sleeper (or tie [US]) in this case, presumably. One of the sites I came across had a photo showing yellow paint on the sides of the rails, whereas the first (Belgian) site below refers to sleepers painted white.

Je repère d'abord ce qu'on appelle la TRAVERSE D'ÉCARTEMENT (le gros trait entre les deux voies qui marque l'emplacement où je descends en dessous de 53 mm - dans la réalité, il s'agit souvent d'une TRAVERSE PEINTE EN BLANC posée entre deux voies JUSTE À L'ENDROIT OÙ L'ENTRAXE DE VOIES PASSE EN DESSOUS DU MINIMUM REQUIS). LE WAGON NE PEUT PAS DÉPASSER CETTE LIMITE SOUS PEINE D'ACCROCHAGE PAR UN AUTRE WAGON ou locomotive passant sur la voie adjacente. Le
http://astrain.skynetblogs.be/post/6567839/122008--les-mecan...

FOULING POINT - A fouling point is THE LAST POSSIBLE SECTION ON A TRACK THAT YOU CAN BE ON BEFORE HAVING A RISK OF BEING HIT BY ANOTHER TRAIN TRAVERSING THE SWITCH.
www.scanbc.com/wiki/index.php?title=SkyTrain - Similar

In the engineerium various repairs and varnishing was carried out to the doors of railcar 50599, continuing the work begun yesterday. At the south end of the line, the S&T Dept spent the day putting in the point connections and facing point locks for the Duffield south ground frame. This is now largely complete and there is only some outstanding work on the north frame to be addressed. Around the yard various FOULING POINT MARKERS were put in, and these do not relate to dog walking. [héhé, someone with a sense of humour like my own ... well, I like to think so ...]
http://wyvernrail.blogspot.com/

I noticed that MARKINGS have been applied to the rail webs in the Oxnard yard, and short plastic cylinders with retroreflective bands have been installed between the rails. These seem to delineate the FOULING POINTS AT SWITCHES. Seems to me to be a really good idea, eliminating guesswork in foul weather.
http://www.trainorders.com/discussion/read.php?1,2051674

• Does anyone have any info they can share on FOULING POINT MARKERS and those railroads that used them? Photos would be great if you had any. ...
cs.trains.com/trccs/forums/t/151352.aspx - Cached
• standard for FOULING POINT MARKERS throughout the national rail network, wherever they are ... should mandate the use of fouling point markers at crossing ...
www.rssb.co.uk/.../Formal Inquiry Recommendations Report 20...