The best way to check if any coupons are valid is to call before showing up. I have learned this helps save time and embarrassment on your end. The hostess on the phone will know if it is valid or not
If you found them in the newspaper or coupon section, they are most likely real. If they are online, check forums for others who have used them. Or call Mortons!
Usually, if you call the company themselves in this case Morton's Steakhouse, they should be able to give you indication as to if it is a real coupon or not.