SPAD mitigation at Brentwood Yard

While riding north on B1 track today, I noticed two new signs marked “SIGNAL B99 06 ON LEFT”, one at the north end of the platform at New York Ave., and one in the right-of-way. I assume this is a SPAD mitigation measure linked to recent incidents. As far as I know, this is the first time signs of this nature have been installed on the Metrorail system, although they are common elsewhere.