Using the Quote Marks
These quotes are a tool, but they also contribute to the design of a slide. They are most effective as ghosted/watermarked objects behind quoted material. Instead of using actual font quote characters, which have an enlarged field, use these quotation marks and fills, lines, and transparencies can be applied. The quotes can also be stretched to the perfect size instead of the trial-and-error method of applying a font size. They are graphics instead of text elements.
Customizing the Quote Marks
If you want to change the size/shape of quote marks, be sure to group the start quote and end quote and resize both together. Once resized, ungroup to proceed with other customizations.
Use the ghosting/watermark formatting guidelines. For light backgrounds, choose a light color (slightly darker than your background) from your palette for the quote marks. For dark backgrounds, choose a dark color (slightly lighter than your background). Write the text for the quote and place the start quote and end quote appropriately around the text. See the example above.
Since these are ghosted/watermarked, it's probably not a good idea to make them too prominent. Resist the urge to apply 3D.
Similar to 3D effects, it's probably not a good idea to make the quote marks too prominent. Resist the urge to apply shadows.
Gradients, patterns, and pictures
Rather than apply gradients or patterns, apply transparency to the quote marks. This is especially useful if your background has some gradients, pictures, etc. The background will bleed through and be visible through the quote marks.
Just have these fade in with or after your quotation material appears. The quotation is the focus, not the quote marks. Be conservative.