The amplify icon is not limited to side schemes. It can be found on obligations, minions, attachments, and more.
If there are any amplify icons in play, when a boost card is turned faceup during an enemy activation (for both attack and scheme), add one additional boost icon to that card for each amplify icon in play.
You can remove amplify icons, by removing the card that has them printed on.
Does amplify works only when a villain schemes or attacks?
Yes. Amplify works only when a villain’s activation.
Do I count the amplify icons when counting boost icons outside villain activation boost? For example with Scarlet Witch’s Hex Bolt?
No. Cards and abilities that make you count boost icons outside villain activation, for example Hex Bolt, the amplify icon does not come into effect.