A backward 3, formally known as the Latin capital letter Ezh reversed, is one of many special characters that Microsoft Windows users can place into their documents despite its absence from standard keyboards. You may access this symbol, in addition to many others, through a program called Character Map that comes readily installed on Windows computers.
Access Character Map by clicking on the Start icon located in the bottom-left corner of your screen and then clicking All Programs > Accessories > System Tools > Character Map.
Scroll down until you see the backward 3 symbol. Click on the symbol and then click "Select" to drop it into the "Characters to copy" box. Press "Copy" to place the symbol on your clipboard.
Click on the area of your document or text box where you would like to put the backward 3 and press Ctrl+E on your keyboard to paste it.