For delivery, they use both DHL and FedEX for the U.S as mentioned here:
https://support.ledger.com/hc/en-us/articles/4403013285137-How-long-will-it-take-for-my-order-to-reach-me-?support=trueThey do use COLISSIMO still, but not for the U.S.
As for your second question:
WILL I NEED TO SIGN A RECEIPT WHEN MY ORDER IS DELIVERED?
Yes, by default both the standard and express delivery methods will require you to sign a receipt when the product is delivered to your door.
What if I do not wish to sign a receipt?
You can contact the carrier to cancel a signature required.
In this case, please note that carriers won’t accept claims in the event of the product being delivered to the wrong person/address or left at your door.