Coinbase bars paid advertising on its own brand terms and requires consent before you send anyone your link, but does not ban public posting.
What the clause says
Coinbase prohibits promoting your referral code through paid advertising based on Coinbase or Coinbase-related keywords, including bidding on search ads containing the name or using Coinbase branded terms in ad copy. The stated penalty is unusually specific: your referral code is deactivated and every referral that came from the activity becomes ineligible.
Consent, and where it does not reach
Coinbase says that when you communicate your link by text, email, or any other channel you may only contact people who have consented to receive it, and that you indemnify Coinbase against claims arising from the message. That governs contacting a person. It is not a rule about posting a link somewhere and letting people find it, and Coinbase does not address that either way.
The cost falls on your friend
Coinbase states that anyone joining through a referral is not eligible for its New User First Buy Spin The Wheel incentive, nor for First Trade and Trade Eligible promo codes. So a referral can leave the person you referred worse off than signing up alone, which is the opposite of how these programs usually work and is worth saying before you send the link.
Do not read the Canadian terms as yours
The same page carries a separate Canadian section with its own numbers, including a ten referral limit and a CA$30 trade threshold. Those govern Canadian residents only. The ten referral cap frequently quoted for Coinbase comes from there.