Does anyone know of any sumptuary laws from the period that would forbid someone from the merchant class from wearing a crown, tiara or coronet?
From my understanding, sumptuary laws pertaining to non-clergy didn't really come into play until the late 13th century.
However, it's not a big leap to guess that the evolution of such laws came from what is accepted behaviour anyway; even if such laws don't exist in 1220, or don't exist in the area where your saga is, that doesn't mean a noble isn't going to take offence at the merchant's choice of clothing and concoct their own punishment as they see fit.
It opens up another interesting thought: where do magi fit in all of this? Is a noble going to take offence at a magus who chooses to wear a crown? I'd say probably yes, and as such the choice may even run the risk of 'endangering your sodales' if not handled delicately.
Depends on how the crown was made to look, also, I suspect.
Well, even kings didn't wear crowns as a fashion choice. They are ridiculously uncomfortable. They were ceremonial garb.
As to tiaras and so on...varies by place, but I'd note that seeing women's hair in many places was considered about the same as them having their breasts exposed. A lot of women wore scraves over their heads held in place by something, and you could call the somthing a circlet or tiara or fillet if you liked.
Crowns are ceremonial garb. Crowns of Quality are a +5 to making people respect mah (nonexistent) authoritah.
(The character to whom this would apply is also looking into a dress with emeralds sewn in, but except possibly among the French nobility, inspiring love and passion isn't a tool for every situation.)
You do not need to look for predecessors of sumptuary laws in the area of your campaign for this. A Western or Central European 13th century merchant wearing a crown or diadem would need more than the bonus of an item of quality giving +5 to gain respect, authority, if he were to walk with it in a town or over the countryside plying his trade. He would wear a symbol of authority incongruent with being a merchant, after all. Really trying to usurp such authority led to a short and exciting life (see e. g. en.wikipedia.org/wiki/Tile_Kolup ).
Should he dress up that way only in a covenant, results depend on that covenant's culture and mundane contacts, though.
Cheers
Also keep in mind there are exceptions to all of this- for example an actor portraying the part of a king can certainly wear a crown, though many a noble might wonder at wearing one that is not wooden or at least a base metal painted over...
... of course if you are using shape bonuses for such a stage crown it could probably be worn much more freely as well...
Have a look at en.wikipedia.org/wiki/Medieval_theatre to see the extent of 13th century theatre. Any kind of professional or regular actors would be white ravens in Mythic Europe.
Cheers
You wouldn't have to be a professional to have it as a reason to wear a crown, so long as you only wore it publicly during the appropriate times. In terms of excuses to have one lying around it certainly fits better...
There are other, more common reasons to have a fake crown: like being a sculptor, gold- or copper-smith, or organizing funerals of nobility. The topic of this thread, however, is 'Wearing a Crown?'.
Cheers
Would goldsmiths have crowns sitting around on spec, like this? I imagine they are guarded pretty heavily during the whole process of creation...
That is most unlikely. But just like copper-smiths and sculptors they can have models of crowns made from wood, base metal or alloy in their shop.
Cheers
Were there head-rings that existed simply to hold your head covering to your head? I thought this was the way traditional Saudis got their head-scarves to stay in place (ie, an iron ring that sat on top of your head, on top of the scarf.) That would probably be OK to have.
The question is whether a crown that is not a crown is a crown; that is, can these noncrowns be considered crown-shaped for the shape bonus?
Just enchant a proper crown to be invisible. 
Cheers
Remember that magic accepts a symbolic representation. Wearing a miniature crown on a chain around your neck would be accepted.
Clever; however, this doesn't work for an Item of Quality crown. Using a clothing or jewelry item as a social tool generally involves wearing it openly.
Unfortunately, a crown only really works as a tool for a noble (or someone acting as one).
Quite so.
Cheers
This just gave me a sudden thought for a Tribunal proposal: establishing a formal coronet to be worn by magi as a(n easily enchanted) symbol of their status.
perhaps a conical shaped device decorated with moons and stars?