According to the protocols, the Archdiocese is to make a 'good faith effort' to secure a signed attestation from each 'clergy member' who is 'working within the Archdiocese' by March 31, 2015. So, priests certainly don't need to rush to sign and return the document. I can't see how any canonical penalty can be imposed upon a priest or deacon for failing to sign, whether the refusal is the result of principle or guilt/knowledge. In fact, it is possible that the Archdiocese met its 'good faith' obligation simply by sending out the document to each member of the clergy.
The attestation, which you can view here, requires a priest, deacon, or bishop to attest that he has not 'sexually abused a minor at any time', nor does he have knowledge of any other priest, deacon, bishop, or employee of the Archdiocese having done so. The language of the document is vague to the point of being problematic. Moreover, as I have said before, I simply do not see the point of this. No one will be safer as a result of this document, whether it is signed or unsigned. Surely the time and effort spent sending these to hundreds of clergy could have been put to better use.