Its the FSR design (The one that Specialized patented), does not activate with pedaling or braking.
On 2004 a guy from Austin (Hammerhead Bikes) convinced Titus to make a run of the RacerX´s with 100mm of travel instead of the usual 80mm, this is one of those frames. I used it for about six months back then and the sited in a closet for 5 years.
It has a Brand new Fox Float shock with lockout.
I am also thinking on selling just the frame for around a thousand.
Saludos