It is considered quite tacky to mention gifts, gift registries, or a preference for cash rather than gifts, on your invitations. If guests have questions, they know to ask the hosts of the event about these concerns.
Putting a note about gifts on your invitation makes it seem like gifts are being demanded or expected − when the act of giving a gift is always voluntary and not obligatory. You also do not have the right to demand that guests buy you something off of your gift registry. If your aunt wants to give you a weird fertility statue, you just have to accept it and send a thank-you note. That’s how gifts work.
If you would prefer not to receive gifts or have guests direct a donation to a charity in lieu of gifts, we think it is appropriate to include this on an invitation, because this is a more unusual choice.
If you are worried about this issue, we think this is one of the best reasons to create a great wedding website. It is appropriate to include information about registries and online links on your website. Guests who want this information can seek it out there, especially if you include your website address on your invitation. Most of our clients do this.