Icarus213: I think we all missed the point of Miami's question. Of course if you can see it's outline you can guess at it's size, but I think the question was, are there any factors that seem to be consistent genetically with a big dick? I am sure we have heard this one before, too.
I can only rely on examples of guys I have seen in person, of course, but the endowed ones appear to me to have sharper features, low body fat, longer fingers/bigger hands compared to their body size, and sometimes a "thicker" build- not always muscular, but more body tissue. I don't think shoe size, nose size, even body size, etc has much to do with it. If you see a lot of naked guys day to day, you can just guess by looking at someone what size he will be- there is a certain genetic profile he will fit by his other features. Hard to explain in writing, but take that for what it's worth.