As others pointed out, finding our system isn't that hard, they can just look in our MotD. What we don't want gankers knowing is, the "when" of what we're doing, mostly so they can land their gank fleet on top of us as we're landing on the next gate, which is where we are vulnerable.
I'd be really interested of how you'd hide the timing of a warp to the next site, or completion of a site, or when we're taking a gate, or what site we're warping to next, without a stream delay...