If you'll notice the dictionairys definition for Sign, Mark, Token, and Symbol are all one and the same!!!

Deuteronomy 6:1
 Now these are the commandments, the statutes, and the judgments, which the LORD your God commanded to teach you, that ye might do them in the land whither ye go to possess it: 2  That thou mightest fear the LORD thy God, to keep all his statutes and his commandments, which I command thee, thou, and thy son, and thy son's son, all the days of thy life; and that thy days may be prolonged.
Deuteronomy 6:6
And these words, which I command thee this day, shall be in thine heart:
7 And thou shalt teach them diligently unto thy children, and shalt talk of them when thou sittest in thine house, and when thou walkest by the way, and when thou liest down, and when thou risest up.
AND THOU SHALT BIND THEM FOR a UPON THINE HAND, AND THEY SHALL BE AS FRONTLETS BETWEEN THINE EYES.

Deuteronomy 11:8
Therefore shall ye keep all the commandments which I command you this day,
16
 Take heed to yourselves, that your heart be not deceived, and ye turn aside, and serve other gods, and worship them;
18 Therefore shall ye lay up these my words in your heart and in your soul, AND BIND THEM FOR A UPON YOUR HAND, THAT THEY MAY BE AS FRONTLETS BETWEEN YOUR EYES.

So let's pause for a moment... As you see so far God's commandments and statutes will be binded upon your hand and forehead...

Interesting... Let's continue...

If you'll notice as we continue God includes His Sabbath and Holy Days in this sign/mark.... And you'll also see "WHY"...

Notice in Exodus chapter 13 God includes the "Feast Of Unleaven Bread" in this sign or mark... Notice...

Exodus 13:3
 And Moses said unto the people, Remember this day, in which ye came out from Egypt, out of the house of bondage; for by strength of hand the LORD brought you out from this place: there shall no leavened bread be eaten.
4  This day came ye out in the month Abib.
5  And it shall be when the LORD shall bring thee into the land of the Canaanites, and the Hittites, and the Amorites, and the Hivites, and the Jebusites, which he sware unto thy fathers to give thee, a land flowing with milk and honey, that thou shalt keep this service in this month.
6  Seven days thou shalt eat unleavened bread, and in the seventh day shall be a feast to the LORD.
7  Unleavened bread shall be eaten seven days; and there shall no leavened bread be seen with thee, neither shall there be leaven seen with thee in all thy quarters.
8  And thou shalt shew thy son in that day, saying, This is done because of that which the LORD did unto me when I came forth out of Egypt.
9  AND IT SHALL BE FOR A UNTO THEE UPON THINE HAND, AND FOR A MEMORIAL BETWEEN THINE EYES, THAT THE LORD'S LAW MAY BE IN THY MOUTH: FOR WITH A STRONG HAND HATH THE LORD BROUGHT THEE OUT OF EGYPT
10  Thou shalt therefore keep this ordinance in his season from year to year
14  And it shall be when thy son asketh thee in time to come, saying, What is this? that thou shalt say unto him, By strength of hand the LORD brought us out from Egypt, from the house of bondage:
16  AND IT SHALL BE FOR A UPON THINE HAND, AND FOR FRONTLETS BETWEEN THINE EYES: FOR BY STRENGTH OF HAND THE LORD BROUGHT US FORTH OUT OF EGYPT.

So there you see in veres 9 and 16 the reason for the sign...