Not a stupid question at all!
The answer to your question is not all that simple. There are the A B C D E s of melanoma, and they are a fairly good guideline to follow. However, they are not concrete. But a bigger issue can be...denial. Or, simply, that in our society there is a prevalence to not make "an issue" about something. That it's silly to go the doctor for something that is probably nothing, right? It's a hard notion to overcome. However, it's one that is found often.
We are told that melanoma typically is uneven, with ragged borders, multi-colored, and large in size. Well, I had 3 moles that fit that description, but a doctor that insisted they were "nothing." I insisted they be removed, and they were indeed "nothing."
Then, 3 years ago I had what appeared to be just a normal mole start growing on my knee. I'm not even sure what prompted me to notice it. But I didn't think it "fit" the description of melanoma: perfectly round, crisp, sharp border, less than 1/4" in diameter, dark brown in color. Just a mole, right? Except something about it looked...strange. I couldn't put my finger on what it was, exactly. A couple of people suggested I go to the doctor, but my thought? Why bother the doctor with a simple mole? Then, it sort of "popped up." That scared me, and I brought it up at my yearly physical. My doctor removed it, did a biopsy, and it came back as melanoma.
There was one very important clue that I missed (and so did my doctor, to tell the truth): when I looked at the melanoma closely, it had a blueish cast with a white center. Yeah, that's it. One of the signs of melanoma that is not widely known that I discovered AFTER my diagnosis when I was searching for what I could have done to know earlier.
In all fairness, I really did suspect something was strange. I didn't really know what: the general look, the quickness of the growth, it was just weird. In the greater scheme of things, I actually took action fairly quickly. I'm thankful for that. But I can understand folks who put it off.
My suggestion? If you see something you think is "not right," get it checked out. Don't feel you are wasting the doctor's time - it's your body. I also personally feel anyone who presents at risk for melanoma (fair skinned, blonde/red haired, large number of moles, large amount of sun exposure/sunburns when young, skin damage) should get a yearly skin check with a dermatologist. At least get a baseline check, so if anything does develop, you have something to measure against. And everyone, no matter their situation, should do regular skin checks on themselves. It doesn't take that long, and can be done when coming out of the shower/bath. Most melanoma is discovered by the patient, after all.
I know this is probably more information that you really wanted, but it's a cause I'm rather passionate about.
If you have any other questions, let me know!