Wake Island:

At the Wake Island beach, there is a little Toy-Dinosaur. It looks like the toy dino, that 'Jono' Miller (Corporal Jonathan “Jono” Miller, 1^st Marines Tank Battalion) received from his son in the single player mission "Operation Thunder Run".
I guess it is a sidekick to MW2:
In a forum (guess it was at http://boards.4chan.org) a CoD Worker wondered why CoD Didn't sell that good as it used to, and they said: "Because the lack of dinosaurs".
 

Here is a pic on WakeIsland:

...and in the single player “Operation Thunder Run":

And a YouTube Video:

UPDATE:

SpotTheOzzie released a video, where he spottet all 5 dinos. In a >>Top Secret<< Document on the map, there is a objective description, that refers to theexistance of 5 or 6 dinos on the map.
After intensive searching, he came to the end, that there are only 5 :-)

Here is the video:
 

 The dino number 6 is found! Great job and KUDOS to Ozzy and the carnage guys:

Somewhere on Wake, a player found a memorial board:

"To those who fought here in 1942, BF2, 2142 and 1943. We are grateful. DICE."

Battlefield 2143 under development?

Maybe it is just joke - or is it a hint? One container on Wake Island (included in the DLC "Back to Karkand") shows the numers "2143".
In the past, developers used hints like these to show, what they will bring in the nearer future.
So we got the numbers 2142 on several parts of the Battlefield 2 Booster Pack "Armored Fury".
For example here:   Read more about it here: Battlefieldsecrets.com - BF2 Vehicles

Here is a pic of the suspicious container: 

We will keep a eye on it in our easteregg section of BF3 Maybe its a hint - but maybe, it is just a number :-)
If it is true, I guess it will be some sort of Add-On, like the "Vietnam" pack for Bad Company 2.