I usually find this kinda question hard to answer 'cos it's all relative (unless there's some specs somewhere that defines "basshead" cans to be +dB from xHz -> yHz?).
Again, relatively, there is bass in these headphones more than the SigPros IMHO (need to really confirm when a proper SigPro is sent to me). But bear in mind that the SigDJs are released with a bunch of other new headphones from other companies so relatively, it may not necessarily be the most bass-heavy amongst its new peers (or competitors I should say).
If you look at the V-Moda M-100 thread (which the M-100 already has quite a lot of bass), owners are further adding Digizoid to the chain! So I think the definition of "basshead" is changing still.