The academic research indicates that, in general, buy-backs are...

The academic research indicates that, in general, buy-backs are a good sign and a harbinger of above average returns for stock holders.
Management engaging in a buy-back is the opposite of splurging spare cash on some empire building acquisition that doesn’t work out in the end.
It amounts to the company saying that of all the investment opportunities that they can see, buying back their own stock at the prevailing prices is as good as any.
In making that decision, management has the benefit of all the inside information that they know about their own company’s prospects.
It’s trading with inside information that is allowed.
If a company has the necessary cash and sets out to buy back 5 or 10% of its stock that will obviously have some effect on the market for the stock.

However, PME is somewhat of a special case because of their high PE.
They never have enough spare cash to affect the market by force of money.
Rather, for PME a buyback is just a signal..
PME is saying that, knowing what they know about the business, the shares look like value to them.
Given PME’s long term price chart, it’s obvious that any share that they have brought back in the past have been good investments.
However, if you go back and check the detail, they didn’t buy at local peaks, rather they tended to buy at local troughs.
Investors could have done worse than taking their cue from the company’s buyback purchases.
Of course, a decision to buy back stock can be a self-fulfilling to some extent because the fact of buying back shares will affect the market if the market believes the signal that is being sent.
Has PME got it right this time?
You will have to ask that well known Italian gentleman.

Here is some further reading.
“Share Buyback and Equity Issue Anomalies Revisited”
http://www.dimfunds.com/wp-content/uploads/2016/03/Share-Buyback-and-Equity-Anomaly-Revisited-Feb-2016.pdf

Cheers