"Universal" symbols

I detest the things.  OTOH, I am now faced with using them.
So, I am trying to minimize the number of different symbols
as a courtesy to my users.
[Note that these have to be understandable regardless of
sensory modality]
I've opted to use (excuse the ASCII art):
-> ]   generic input
[ ->   generic output
(+)    power entry, positive polarity
(-)    power entry, negative polarity
Note that I have deliberately avoided the convention used
on barrel connectors:
+ ---( O--- -
- ---( O--- +
because it is impossible for SIGHTED people to read (when reduced
to whatever size the packaging requires -- leaving room for all
the other crap that folks want to adorn their products with
(e.g., legalese).  Imagine trying to make a version that
someone with no/limited sight could discern!
I figure a + or - in a circle is more than adequate AND can
be reproduced at a larger scale than all of that other cruft.
I've used other symbols in a conventional manner (e.g., ^ for "this
end up").
But, other (ISO/OSHA) symbols seem to stump the folks on whom I've
auditioned them.  E.g., "hot", "high? voltage" (I was surprised at
that!), "danger" (also somewhat surprising),  etc.  Any guidance on
how to more reliably convey this sort of information without
requiring the user to "discover" the indicated problem "the hard way"?