Can I just say this...as far as I'm concerned, they aren't all that magnetic and unforgettable. If they were, then Leo's influence is probably working at them more than they realize. The timing of your question about magnetism and unforgettability coincides with a predominate Leo influence, so nobody should lose sight of its involvement.
All Fixed Signs, which include both Scorpio and Leo, exhibit some kind of indelible quality which captivates persons. Which people are most likely to be drawn to which of the four Fixed Signs depends on which Elements are predominate for them. Where Earth is the predominate element, those subjects will be very drawn to Taurus as the picture of taste and beauty. Where Air is predominate, those people will find Aquarius highly enriching. Leo will light people's fires.
Scorpio would have the biggest hold on Water personalities. Wherever Pisces, Cancer, and Scorpio are predominate. Sensitive, spiritual beings who are drawn to Scorpio's cool calculated demeonor, and ability to work at their psyche. It isn't a combustible sign where it is Fixed Water, and it isn't going to draw everybody in. Just the ones who are having a spiritual or emotional void filled by it, or who need to be entrenched by something as a way of purging their temporal impulses or worldly attachments.