If I wanted to do this, I would first figure out what the alarms are by reading a manual, or asking someone like a local repair shop or someone who has that model year engine. Then I'd google "outboard warning horn decal" to see if I could find any decal at all that has the same warnings. For example, I found a
boat alarm kit. Its a replacement warning horn, but it comes with warning stickers.
If i couldn't find an equivalent decal, I'd make my own using any number of office tools (powerpoint, word, open office, etc, etc). It's not terribly difficult if you have some basic computer skills and a modicum of creativity.
Lastly, I'd look for a source that would make such a label for a price I am willing to pay. Google "vinyl decal" to find tons of options including
FedEx.
If i could not find a source to make the label I created, I'd just print it on an ink-jet and cover it with this :
Water-Proof Label Spray. I doubt that this would last very long on a boat, but printing a label is cheap so you could do it every year. Or you could print a whole page of labels, spray them all at once, and then use them up as needed.
Hope this helps.