Affiliate disclosures - what, why and where
You do not have to worry about using special wording for a disclosure. The point is just to give the readers necessary information – it does not have to be written in legal jargon and in fact, it is better if it is written in plain, easy-to-understand language.
Size, color and graphics should be related to the rest of the website – readers need to be able to pay it full attention without having their focus drawn away from it. For example, the font should be as large as the main text on the page and it helps if it is a contrasting color to any background and the main text.
You also need to remember that people may view your website on different devices. If they are reading on a mobile, they are more likely to see a disclosure when it's included in the actual post than when it is in the sidebar.