The scam is not downloading Signal. The scam will come later when they say "You just got the job! I will send you a check to purchase your remote work supplies".
Do not deposit the check. At all. No matter what. It is not a legitimate check. It will never be a legitimate check. No matter how real the check looks, I guarantee that no company works like this! Do not respond to them. Block their number and ignore them for the rest of your life.
What happens is: The check is fake and you deposit it. By law, your bank is required to credit your account with the check's value within a couple of days. HOWEVER: Just because your account gets credited the amount, doesn't mean the check is fully processed. The scammer will tell you to buy WFH supplies from a "trusted vendor". You are "buying" your supplies from the scammer, using the money credited to your account. Then, in 2-3 weeks, the bank will reject the check as fake. They will subtract the value from your account and you will have paid for your "supplies" using your own money. You will never receive the "supplies" or get your money back. The bank might even suspend your accound because of the fraudulent check.
A youtube channel that I follow actually released a video today about employment scams. In the section where he talks about red flags, compare them to the messages you just received. I bet you'll notice some similarities. https://www.youtube.com/watch?v=K9g-y8wVzws