Pennsylvania's code never names an SR-22, only proof of financial responsibility
Search the financial responsibility chapter of the Vehicle Code, Title 75 Chapter 17 and you will not find an SR-22 anywhere. What it has is section 1783. In its words, PennDOT will not restore a suspended license or registration "until the person furnishes proof of financial responsibility".
It applies after an unpaid crash judgment, an uninsured crash, a habitual offender revocation or a reported conviction. Section 1782 says you can meet it by showing that every vehicle registered in your name carries liability insurance. For a resident, that proof is insurance paperwork you send PennDOT yourself, listed below.
Out-of-state drivers are the exception: their insurer files a certificate
Section 1782(b) of the same chapter covers a nonresident whose vehicle is registered in another state. You give proof by filing a written certificate from an insurer authorized in that other state. PennDOT takes it only if the company signs a power of attorney letting PennDOT accept legal papers for it. It must also agree in writing that the policies meet Pennsylvania terms.
No vehicle at all? The same subsection accepts evidence that you do not own one. This certificate is the nearest Pennsylvania match to an SR-22.
Papers PennDOT counts as proof, including an Assigned Risk Plan application
PennDOT's insurance overview accepts a copy of your insurance ID card or the policy's declarations page. A binder signed by a licensed agent also works. It lasts only 30 or 60 days, so you send proof again when it ends.
If no company will write you, an application to the Pennsylvania Assigned Risk Plan counts once a licensed producer signs it. Section 1741 set up that plan for high-risk drivers who cannot buy cover the normal way.
After a ticket or crash, PennDOT's registration restore page asks for something stricter. You need a letter from your insurer's home office, signed by an underwriting manager or supervisor, saying the policy was in force that day.
Three months off the road after a lapse longer than 30 days
The Insurance Law fact sheet says a lapse suspends the registration for three months. The exception is a lapse under 31 days when you prove the car sat unused. Driving uninsured brings a $300 minimum fine and a three-month license suspension too.
You can skip the registration suspension once in any 12 months by paying a $500 civil penalty. The restoration fee and current proof are still due. Form MV-70S puts Motor Vehicle Registration Restoration at $119.
Insurers must report a canceled policy but need not report your new one, so answering PennDOT's proof letter is your job.
$15,000, $30,000 and $5,000: the floor PennDOT checks
Chapter 17 defines financial responsibility as $15,000 for injury to one person and $30,000 for two or more people. Property damage adds $5,000 per crash. The same three amounts decide when an unpaid judgment counts as satisfied for license purposes, under section 1774.
Your own list sits in the free restoration requirements letter on PennDOT's license suspensions page. If you open it online, print it, because PennDOT will not mail a copy. The restoration letter fact sheet shows that DUI cases add court-reported items, such as finished treatment.