The only valid approach here is to assume your reader does not know which version you are using, and make sure you build up enough context to make it clear.
One context may be to state what Richard Hardy suggested, differentiating between percentages and percentage points. That being said, I've never seen the
%p notation before, so if you use that notation you might want to clarify it as well. Wikipedia suggests
p.p. as other possible notations.
Another context might be nearby numbers. If I say "Inflation went up .2% this year," people reliably understand that that number must be an addition of 0.2% to the inflation rate percentage, as opposed to a claim that inflation has been scaled by 100.2%. This holds true even if I was imprecise in my use of percent vs. percentage points. On the other hand, if I say "murder rates were at 3% last year, but went up 30% this year," you can be quite confident that that was a scaling factor, unless you knew there was some major insurrection in the area.
One of the easiest ways to maintain this context is to say the value in several different ways. If you say "unemployment went up 25%, to a record high of 18%," it's pretty darn clear that you intended to say unemployement rates were multiplied by 1.25. Incidentally, this is where the duplicated legal terms like "null and void" or "aiding and abetting" came from -- they were saying the same thing twice, once in common law speak and one in the official terminology which derived from French law.
We have a similar issue with the nuanced difference between an absolute temperature measured in Fahrenheit and a differential temperature measured in Fahrenheit. The conversions are different because one has to account for the fact that the Fahrenheit scale does not start at absolute zero. Dozens of notations have been suggested to resolve this, but nothing is quite as effective as maintaining a clear context so that the reader understands what you meant.
Communication is all about context, and different phrasing will mean different things to different people.