Y'know d.rat, I'm of two minds on this.
One, I says go with your gut. Paranoia has saved my grits on more than one occasion...and provided comic relief for many more.
Two, I says t-shirt? ARE YOU KIDDING ME? I assume you live in America. If not, then who knows wtf you're in for if you get caught. I've worn t-shirts that've said some pretty onery things...it's just a t-shirt. Many people will not even notice you have something written on it becuase, it's just a frikkin t-shirt.
I remember when dre/snoop hit in 93...I had a chronic leaf on every hat I owned. My mom told me how retarded I was and how I was going to get in trouble, advertising my criminality.
I never once had a cop do a double take and be like, 'hey you with the hat! come over here and let me see if you got any of that reefer on you...' Of course, they'd always yell when I'd drive off in their patrol car, hat or no.
Basically, you're feeling like you may get popped b/c someone will see the shirt, get it, make the stretch, be correct (cause imagine an otherwise upright individual making a FALSE accusation: 'she's wearing a shirt and so she must grow pot!' Chill...I got it from my hippie uncle in frisco...) and then want to rat you out for 'alternative horticulture'...it just seems farfetched to me, so yeah...I think you're being paranoid.
All that being said, if the shirt is an issue to you for real, maybe y'all shouldn't be growing pot, much less spending forever together.
2 cents + my opinion = will not buy you coffee.