Reiki symbols look like ordinary Japanese writing but actually have great power behind them. The question is whether or not they can be effectively used by a person who has not been attuned to Reiki? Let us take an example.
Imagine an electric switch. You have seen and used it innumerable times. It is there on the switchboard in every room that has electric connection. If you push the switch, the electric appliance connected with it starts working but if the same switch is disconnected and lying on the table disconnected from the electric circuit, would that work to switch the appliance on? It will not, even though it is the same switch. Unless it is connected to the energy, it wouldn’t perform the function for which it has been designed. So is the case with Reiki symbols. They would work for a person who has been consciously connected to the universal energy through the process of attunement (whether through Reiju or Western style). For others, they are of no use at all.
The Reiki symbols are written in Japanese writing system called Kanji, which is not as easy to remember as other English alphabets. The symbols are to be drawn or visualized in their particular shape and sequence. The chances are that one might draw them incorrectly. Since Mrs. Hawayo Takata did not allow the student to make written copies of the symbols and they had to memorize them, the chances of mistakes in drawing those exactly in the same shape and sequence could not be ruled out and it was feared that after passing from person to person by heart, some of the symbols would lose their original shape over a period of time, which they actually did. Thus gradually many variations came up. However, you need not worry on this account. It is the responsibility of the teacher to teach the correct symbol to his students. You should use exactly what your Reiki teacher taught you. Do not get confused with many versions.
I would also like to highlight that symbols are mainly a tool for the beginners to gain confidence in carrying out distant healing. Once you have practiced enough, the symbols become redundant and you can stop using them. You can effectively carry out healing even without those.