Yes, a judge can. The law does not specify what constitutes a "signature," and people can use a variety of different formulations, ranging from all names spelled out to just first and last initials and everything in between.IF someone felt that the judge who purportedly signed it did not in fact sign it--e.g. a clerk or a police officer signed, scribbling down the judges initials--that might constitute grounds for both challenging the order and possibly for the imposition of some form of  liability against the person who did it. However, absent some reason to think the judge's initials are not in fact the judge's initials, there're no problem with them the judge just using initials.