Here is an interesting comparison of Cortana over the course of the 4 halo games:
PTesh adds his dulcet prepubescent tones over the top of one of the new trailers for weapons...
Try upgrading your browser to Google chrome (you wont regret it). There is probably an IE...
A brighter highlight of MC's left boot shows us Marcus R. Lehto, Halo's Art Director's initials. He is the man behind the chiefs armor skin, apparently to show the people that the armor is HIS property. Or just leaving his signature there to show he designed the Armor and leaving that as his credit. Also like said in the comments by "AnEProGamers" His signature is also engraved on Master Chiefs boot even as the Toy Figure.