Can I pin myself if I’m on PCs leave? Or should I wait to arrive at my new unit?

As a current Troop 1SG, I would have a problem with you doing it yourself. As a "new" NCO there is a right of passage with your promotion ceremony that you need in order to completely understand what putting those stripes on means. Just my two cents from my foxhole!

As the Major told you, wait. That way they know it is done in the way they want.

In 24 years, I've only had one "Promotion Ceremony".
The rest, I pinned myself.
If the orders are printed, you are a Sergeant.
Introduce yourself as Sergeant and make sure you include copies of those orders when you in-process with S1.
(If the orders are already in your OMPF, then this isn't even a question.)

Getting pinned is a unit thing. I can see this both ways. As a Reservist I got my LTC orders in the mail. My unit was in MO and I lived in TX, and performed my Reserve duties in TX, so I pinned myself. When I was promoted to COL I was between units, meaning my promotion was effective after my last drill at my old unit and before my first drill at my new unit. I pinned myself, so that most Soldiers wouldn't know that I was a newly promoted COL. When I arrived at the unit the CG told me to put on my LTC rank and that he would promote me in the unit formation the next day. Luckily I decided to bring my old rank with me. Bottom line, since you are enlisted contact your new 1SG and ask for permission, that way you start off on the right foot.

E-2 through E-4, pin it on. NCO ranks wait.

You're already getting paid for the increase in rank. I'd just wait to actually wear it. Don't want to risk upsetting the wrong people if they care a lot about ceremony.

Maybe I'm old school - but I think it is very important, if not essential, to have a formal ceremony when you get promoted.. It tells everyone that you have succeeded in your career - your peers, your bosses and most important your family. Having this happen after you get to your new unit is a big plus..it sends a message. On a personal note- after enlisting and eventually going thru OCS my Dad "pinned" me for all my promotions - and the one he missed he was the hospital after open heart surgery. We took a lot of pictures of that one.

Everything will be smoother for you if you show up wearing SPC/ CPL. If you have Sgt Orders, they will promote you right away. This happened with me, for E-8. PCS from AK to KY.

If you're PCS is going to be a short period of time, print your promotion orders, contact your new units 1SG and find out if they can pin you "upon arrival". Make sure you're clear with that so they don't jerk you around and delay your promotion. If they give you anything other than "absolutely, look forward to your induction to the NCO Corps," have someone else promote you first. Pin yourself only as a last resort. But you really want to give your new unit that opportunity.

*Note* Do not pin without orders. Period. Impersonating an NCO is punishable by UCMJ

I see both sides of the coin and I made the E5 Cutoff while on PCS leave and made the E7 Cutoff while on PCS leave. In both cases, I had a little ceremony in front of the mirror and promoted myself. And in both cases, no one cared. Now these were several, several years ago, but I say do what you feel is right. If you have the orders, you are legal and either way it is up to you. Congratulations and I hope you make the NCO Corps proud either way!