If you do, for your own safety, please take it down immediately!
In any gun fight, there are two battles. The first is the gun fight itself. It appears that you are prepared to win that one. If you have that sign posted, you are woefully unprepared to win the second battle, which will take place in a courtroom, and/or in the news media.
Imagine yourself sitting next to your defense attorney--to whom you have forked over your entire life savings, as well as the money your got for taking out a second mortgage on your house--as the prosecutor shows pictures of that sign to the jury and tells them how you murdered "that poor sixteen-year-old boy in cold blood"--never mind that he was six feet tall, 240 pounds, already had two kids by two different mothers, and was threatening you with a knife.
And if your attorney is good enough and does manage to get you off, you will then have to face a civil suit by the "boy's" family. By now your funds will have been exhausted, and your new attorney will want a retainer, so your parents will have to take out a mortgage on their house.
You've done the necessary preparation to win the first battle. Prepare to win the second one also. Start by taking down that sign! Then read up on what to do after the gun fight, too.