The only regulatory restriction on trust advertising for a National Bank is contained in 12 CFR 9.18 pertaining to the prohibition on advertising Common Trust Funds.
Other than that, at least for OCC regulated institutions, I'm not aware of anything. However, be cautious when advertising trust services. You can get tripped-up on the Member FDIC logo and depending on the type of product/service advertised, it might be appropriate to use the not-not-may disclosure. But it all depends.