Mobile Apps and More : Mobile Greetings

How do I know if a mobile ecard is from AmericanGreetings.com or if it is just spam?

All messaging from American Greetings will come from our phone number of (440)373-7423 or (440) 373-7422. No other company can send messages from these phone numbers and American Greetings will not send messages from a different number without notifying our customers first.