Answer:
H.R. signifies a House bill and S signifies a Senate bill.
Step-by-step explanation:
When a bill is introduced it receives a number and a letter before it referring the chamber from which the bill came from. H.R. is used for the bills introduced by the House of Representatives while S. is used for the bills introduced by US Senate.
When the bill is voted in the House it goes to the Senate, it must pass in both houses of Congress before it goes to the White House. It is the US President that gives the final vote on a bill, the president pro tempore is a temporary substitute for the presiding officer of the senate when the vice-president can't attend. When a bill has been passed as a law it is called statute or an act of the legislature.