While these (Unicode, I think) characters - ◖ and ◗ are correctly displayed both on a PC browser and on an android browser, these other - and - are displayed correctly only on a PC browser, not on android. To be honest even in this Sitepoint post I cannot see them correctly.
The following code  and  doesn’t work.
I add a screenshot, where you can see all the special characters working (on a PC browser).
It can be very light, especially if you just serve up the characters you need. Google fonts let you just download the actual characters you need, for example. I’m not sure how to do this with self-hosted fonts, but it could be worth looking into.
However I have a problem with that code: it doesn’t work as expected in android (Vivaldi) browsers.
Even after deleting the browser cache, I still see this
instead of this
A very smart solution. Really. But so far I managed to get it working on a desktop browser, not on an android (Vivaldi) one: nothing appears. Even with a .8em (instead of .5em).
EDIT
Maybe is a cache problem (server side). I will see later.