Pafalafa-ga is correct about the lien.
To answer your second question, IRS doesn't file the lien
just when there are visible assets. IRS files the lien because
there is a balance owed. This will show up on the credit report...
though sometimes it takes while to appear.
I am just working on a case where we got all the balance
due information from IRS and they paid it off, only to learn,
after they refinanced their home and used the money to pay
IRS, that there was another lien out there that no one found...
for over $60,000! Even the title company wasn't aware of it.
So, as I say...it may not always make it to the credit report.
The best way to find out what someone owes to IRS, and if they do?
Have them sign an IRS Form 8821 - Tax Information Authorization
Even then, you have to enter the years - and if you don't know what
years might be in arrears, you could miss the information.
You could request TXMOD or MFTRA-X reports (see explanation here).
But, again, you need to know the years to see.
Frankly, without the cooperation of the person whose record you
want to see, there's no way to learn if they owe money to IRS -
unless the liens have been filed.
And thank goodness for some small bit of privacy we've got left!