The problem with just copying the hand signs is they may not be a true representation of the word. An example: If you want to convey the word "job," it would be spelled, J-O-B. But its hand sign is very different--it is only one sign, not the three individual signs for the letters. True signing has individual signs that carry the meaning of specific words, so one rarely spells words out. If you spelled out each individual word, it would be inaccurate signing.
The construction of phrases isn't the English form either. It is actually the French form, where the noun comes last. Example: If you want to ask someone their name, you would not spell out "w-h-a-t i-s y-o-u-r n-a-m-e?" or sign, "What is your name?", but rather give the three individual signs for "you-name-what."
Signing changes in differing geographic locations too, although the signs may be related to each other. To make matters worse, people use different types of signs depending on how they were raised. Some methods of signing are totally different, making communication difficult to impossible for even experienced signers. Your best bet would be to use standard American Sign Language.