Albert Barnes Commentary Psalms 86:17

"Show me a token for good, That they who hate me may see it, and be put to shame, Because thou, Jehovah, hast helped me, and comforted me." — Psalms 86:17 (ASV)

Show me a token for good ... - Hebrew, “Make me a sign for good;” that is, Do that for me in my trouble which will be an evidence that you do favor me, and will save me. Let there be such a manifest interposition in my behalf that others may see it, and may be convinced that you are God, and that you are the Protector and Friend of those who put their trust in you. We need not suppose that the psalmist refers here to a miracle in his behalf.

Any interposition which would save him from the hands of his enemies - which would defeat their purposes - which would rescue him when there seemed to be no help, would be such an evidence that they could not doubt that he was the friend of God. Thus they would be made “ashamed” of their purposes; that is, they would be disappointed and confounded; and there would be provided a new proof that God was the protector of all who put their trust in him.