Can Missionaries Protect Their Initials?

Dear Rich: I am the founder of a lay missionary organization. We use the initials SMM that shows our affiliation and membership to the Society of Missionaries of Mercy. I have been told by the Society of Montfort Missionaries that they claim that SMM can only be used by their membership.  Please advise me. Should we change our initials or inform them that you can't restrict the use of initials? As we discussed in a previous post, asserting trademark rights over initials is possible but often difficult. We've also discussed protecting names of religious organizations. We note that even if the Montfort group did chase your organization into a U.S. court, they would need to prove that U.S. consumers  are confused by the mutual uses -- something that might be difficult because the other Montfort group appears to be based in India (and perhaps associated with this Scots group). So, in summary, we think there are some hurdles if the  Montfort group wants to obtain a U.S. court order to stop you.
From the legal to the cosmological. Resolution of your question goes beyond legal issues and into trade customs and religious hierarchy. Catholic religious organizations appear to rely on their initials to distinguish themselves from others. This chart, for example, lists 800 such abbreviations. We cannot say whether a change of initials is required to serve purposes of this Catholic exonumia but we hope this matter can be resolved on the basis of religious custom (not U.S. trademark law) and, of course, in the spirit of brotherhood upon which these organizations are founded.