would love to see some guides on how to make more serious looking banners
Pirates of the Burning Sea has guidelines posted so flag makers know what colors they can/cant use, mainly dealing with saturation levels. Same rules pretty much apply to Medieval heraldry
http://www.burningsea.com/forums/showthread.php?t=19608
In terms of saturations, the artist should know by feel. There is a history of paints and dyes out there, if one cares to look. Also, people/ artists should be testing their shield in game (by player side modding the banner files for testing), and choosing colors that are 'paint' colors, and not PC backlight colors, or modern fluoresents (duh) - think of your palette limited to natural colored poster-paints....
Here is a good place to start, (for European factions)
http://www.rameset.com/heraldry.htm for the traditional rules BEYOND colors, if you havent already a basic knowlege of what is, and isnt proper and/or common in heraldic design. The colors are PC colors here and ARE way too bright, but they are
representative of the 'hue's allowed, according to heraldic law.
o
-Notice especially the basic law that a color cannot be placed on a color, and a metal cannot be placed on a metal- Its alittle more complex than that, in that each field/color/charge is aseperate 'layer' placed one upon the other, but if you want to understand that, read the link, and look some more up, its all there for your casual study. - This, and some common sense in natural color choices, along with eliminating modern cartooning style and photo-realism, would go along way on making your Heraldic design, and the whole pack, spectacularly accurate, within reason.
These rules I think would/should apply to western european civilized factions in CRPG warband. - Not necessarily rules for submission, but guidelines to adhere to, unless you want a historically inaccurate design, or if your faction isnt a civilized western faction.
I would argue, depending on your Guild's RP geographical origin, the best way to go about your own guild's Heraldic Arms, is to consider its origins, make/take a symbol/colors that already represented it prior to crpg/WB, imagine it evolving into a coat of arms in a cultural context over a period of years or centuries, study the basic rules of color, metal and charge (symbol) in the link above (or other like sites) , and then apply that to a shield, using the laws of heraldry (if your faction is civilized and western) and voila! theres your Guild's Arms for CRPG....