Isaacsac,

You may also want to send the link for this SCF issue to WMATA using its comment form:
http://www.wmata.com/about_metro/contact_us/ridercomment.cfm

During the warmer months, DC Dept of Public Works (DPW) removes graffiti quickly (days). I think it may have slowed or suspended its graffiti removal for the colder weather.

Contacting WMATA, too, will increase the chance of a prompt resolution.