Some examples for clarity:
$20 (good)
20$ (bad)
Now, I understand the difficulty for some to grasp this concept since, even when written correctly, we still say (using my example) "twenty dollars". Yes, this can be confusing to 2nd graders and below. But, the dollar sign first is correct.
I also understand some people will want to argue this point with me. Please realize that, if you do, you will identify yourself as a moron.