Can you please elaborate in detail as to why there is an apostrophe d after the +1?
Clicking "+1" means you're adding yourself to the number of people who support or like this thing.
Clicking "+1" is an action, and plus one is being used as a verb for clicking it.
Usually the past tense of a verb such as walk is walked.
The past tense of performing this +1 action, could be spoken as "plus one-d", which has been written as +1'd.
The apostrophe is often used to denote the omission of something, or in this case to try to improve readability, and possibly an attempt to hide some of the uncertainty of how to properly make a symbol such as "+1" into the past tense.