Open a graphics program on your computer and create a new blank image by going to "File" and "New." Set the dimensions to 300 pixel width by 300 pixel height.
Decide on what type of street sign you would like to create and then choose an appropriate shape to use for it by going to the "Rectangle" tool and holding down the left mouse button. You can select a rectangle, circle, polygon, or one of the many shapes offered.
Position your cursor in the top left side of the new box you created, click and drag across and down to the bottom right side to create your shape.
Click on the "Paint Bucket" tool and choose a color in the "Colors" panel on the top right of your graphics program. Double-click on the topmost square to bring up a color picker, then move your mouse around until you find a color that would be appropriate for your street sign.
Place your mouse over the shape you drew in the new image and click to add the color you selected.
Select the "Type" or "Text" tool and click in the middle of your shape to add text to your street sign. Type either text or a symbol, depending on what kind of sign you are making, and fill it with an appropriate color. For example, if you are creating a stop sign, you would make the text white.
Add finishing touches to your sign, such as an outline around the sign itself or a post.