This line of thinking seems awfully prevalent nowadays among fans, and it strikes me as a bit unfair. Is Chris Davis "suspiciously good" this year or has he finally figured it out and good for him? In the absence of any evidence to the contrary, I prefer to think maybe he has joined the long list of players throughout history who used "improve at baseball" and not "banned substance" as his "drug of choice".
What are good benchmarks for suspicion? Well, one of them, obviously, is "Your name has shown up as part of a ring of illegal activity." The players linked to Biogenesis? OK, you can have your doubts about them -- I think that's fair. These guys are, besides being cheaters, apparently incredibly stupid, as is Biogenesis. Why the heck would a lab, and why the heck would a player, use real names in notes on file? Even Chris Perez was smart enough to have his packages of marijuana sent to his house in his dog's name. Actually, that was pretty stupid too. I can't wait for the Indians to come to Oakland so I can yell, "Hey Chris, your dog called...there's a package..."
Anyway, "doing well" is not tantamount to "probably cheating". What is? The guys who get my attention are the players whose bodies freakishly change. That's legitimately cause to go "Huh?" If I had to irresponsibly pick one guy out of a hat as arousing my baseless suspicion, it would be someone like Mike Morse. Morse has a hulk-like frame that looks like he should be holding Fay Wray in his left hand, not like he came up as a shortstop. I'm not accusing Morse of anything, mind you (why bother until he gets his OBP over .300!); I just wouldn't be super-shocked if someday I learned he was PEDdled something illicit.
Or you could look for players who hit ordinary fly balls that somehow carry over the wall, which is pretty much how the steroid era first reared its head before anyone knew to be suspicious of anything. Nelson Cruz has hit some balls that off the bat I went "Oh good, we got him out" and then "Wait...No...Wha'???" However, I don't need to suspect Cruz because he didn't have the good sense to send his dog to Biogenesis instead of himself.
I don't especially suspect Bartolo Colon, because while he is "pitching too well for a 40-year old" he is also throwing mostly 90 MPH with movement and location, as a 40-year old who has always had great control might do. As someone already caught once before, he is subject to extra testing and if he is taking something that beats the tests then it is likely something less potent that 300 other players are also taking.
MLB has come a long way in moving past steroids and amphetamines. Sure, players will always find new substances and clever ways to beat the tests, but at least the playing field is leveled by thinning the available substances to far fewer. The ones that are being used right now are likely far less impactful and are being used by many, not just by 3-4 guys. Heck, caffeine gives you a bit of an energy boost and some increased reflexes and focus. Thing is, any player can wolf down an espresso prior to first pitch -- not a big deal.
My main point here is, don't suspect someone just because they are performing well. Good ERAs, high HR totals, and "breakout seasons" are not the best indicators of PED use. Strange strength or body type, balls that carry suspiciously well off the bat, inexplicable endurance, or a precocious dog? Now you're talking.