When I was 16 mother found my porn, asked if I was gay, I said yes, she insisted it was a phase. Now she thinks I am completely straight (honestly I am questioning my sexuality I am leaning more towards mostly gay, bi because I do like women in the same ways I like men, just less sexual though.. still sexual.) So... that's that I am 22 now and when I was 17 she asked me about that conversation we had if "I'm good" and I'm like..yeah...now if she had asked if I liked guys I would have been like YEP. I don't see the point in telling them. It's pretty darn obvious I am definitely not straight. My father says I remind him of that boy from house of lies (if you know who that is lol, I am not that femme though). Most people tend to think I am straight. Straight friends I have had for years (5-7 years) forget I am even gay (though questioning this leaning more towards mostly gay/bi)
If it were me, I wouldn't make it a point of discussion to dance around. Just bring it up in regular conversation or reference it. If your mother is trying to avoid it, it may not be best to try to shove it in her face. Just don't hide. I hope I could help. I'm dealing with somewhat similar issues, myself.
I agree with Stillaweirdo. don't stuff it down you're folks' faces. But you can leave subtle hints. you don't need to say anything, cause you already have. maybe while watching tv with your folks, say wow that's a sexy looking guy or something like that. don't hide the porn, rather leave it on the most obvious place. these little subtle hits will help them to realize that it's not a phase!