In legal marketing, perhaps the most tempting rule to violate (at least in BC) is the prohibition on using the name of sitting judges or masters as being former members of the firm. If your former colleague has been appointed to the Bench, it only seems natural to proclaim your pedigree by association. Alas, this would violate Professional Conduct Rule 7.2 in Chapter 14.
Former firm of current judge or master
7.2 A lawyer must not state on any letterhead or business card or in any other marketing activity the name of a judge or master as being a predecessor or former member of the lawyer’s firm.
As every lawyer should know, it doesn’t make it OK just because everyone seems to do it. It may fall within a grey area if you are simply posting “news” that a colleague has been appointed to your website. Just don’t make it a permanent marketing presence.