The SBL Handbook of Style, 2nd ed., contains fairly sparse treatment of how to cite lexicographic sources (§6.3.7), and none of the provided examples address how to cite standard lexica for the biblical languages (e.g., BDAG, HALOT). This clarification is supplied in a post on the handbook’s blog. Footnoted citations should follow a form like:
BDAG, s.v. [entry]
HALOT, s.v. [entry]
The lexicon abbreviation is italicized or not depending on whether it abbreviates the lexicon’s title or the initials of the parties responsible for the work.
For additional examples, information, and discussion, please see the full post on the SBL Handbook of Style blog.