One shaker has three holes and the other has five. All holes are the same size. What do you think?
Put salt in both of them.
Get a pepper mill for the pepper.
Salt always goes in the one with the fewest holes because it pours faster so three.
I agree with alice.
The one with the S on it.
I’m using Sea salt, it doesn’t pour out like table salt.
Salt goes in the one with more holes. You use more of it. I’ve never known anyone in my life who did it any other way. It’s a sure bet when I pick up a shaker the one with more holes has always had salt in it. Unless it’s already indicated by initial or color.
Superman has salt in him?
Yep.
Well, you’ve sort of met some of us.
Heh, is it odd that a significant percentage of things I’ve learned on the dope is that people do things I never would have imagined with food?
Wait, you’re enough of a gourmet that you’re using sea salt but not a pepper mill? 
Salt in the one with more holes. As coffinjumper stated, you use more of it. Pepper is typically used more sparingly.
What’s surprising to me is that this appears to be another “does the toilet paper roll go over or under” debate. To each his own, I guess!
If you look at shaker sets with an “S” and “P” on them, the salt shaker always has more/larger holes. People use much more salt on their food than pepper, simply because a little pepper goes a long way.
I use way more pepper than salt, but I know that the salt goes in the one with more holes. I’m sure if you want to Google salt and pepper shaker images you will see many examples. Personally I use a grinder for both the pepper corns and the sea salt.
Too much salt will spoil almost anything; pepper is much more forgiving. Less holes for salt.
I just followed my own advise and Googled images… lots to support my stance… and just as many that contradict it. So I guess the answer is whichever you put the salt in is the salt shaker. Shake some in your palm first to see how much comes out, and which it happens to be.
I use identical clear glass shakers which elimnates confusion. Originally, both had the same number and size of holes but the coarse ground pepper I like didn’t come out well so I used a Dremel tool to enlarge a few of the holes. Now it is perfect.
The one with more holes has always been for Salt. Look at any salt & pepper shaker set in a restaurant.
I buy my salt in shaker containers. So it’s been a long time since I filled an old fashioned shaker.
In most restaurants I have been in, and households come to that, the salt shaker has had only one, relatively large hole; the pepper has had several holes, but smaller. This is because salt has larger, heavier grains that require a larger hole, but it will go relatively fast through a hole large enough not to get constantly jammed. Pepper will go through much smaller holes, but to get enough of it you need several of them.
Hole size is more to the point than hole number, but, generally, the larger the holes the fewer of them there are.
But anyway, if we are talking about sea salt, in my experience its grains (or flakes) are too large to be used with a shaker at all. You want a salt cellar.
I can’t live without my sea salt and fresh ground pepper. I was tired of my daughter complaining about not having regular old salt and pepper around so I dug these out. They have no markings and are wooden.
Update:
The holes were too small on both so I used a small drill bit to fix em and now the one with three holes is good for the pepper and the one with 5 holes is full of sea salt that comes out just right.