Yep, what James said. We highly encourage using some creativity-- After a while, many can start looking the same because certain design ideas are so popular, but heraldry affords some very creative possibilities, especially when looking at the geometric divisions, sections, and the like.
No familial lineage is necessary. In fact, I'd prefer to keep historical designs out (unless you have a direct, actual claim to it), to avoid conflict with any actual family usage today. Having said that, it's possible you might invent something from scratch, and by coincidence it's one that was used historically. I'm not too concerned about this. In the end, it's really up to you.
We don't require them to strictly adhere to the historical rules of heraldry, but strongly encourage people to stick to them, or only fudge it in ways that make sense. A good rule of thumb to use is whether or not it would pass in the SCA. I registered mine there, just as a precaution to make sure that most of the historical community that cares about such things won't end up using the same thing.
For most members, what I've done is taken the image that they provided, and redrew some or all of it into a template from the Inkwell's coat-of-arms designer program, so they're consistent on the website.
