It's just a warning (from Safari probably) that the sites you are visiting may not be fully trusted.
There could be may reasons why;
The site may still be using http instead of https
The sites security licence may be expired (or be due for renewal).
there nay be something dodgy about an advertisment on that webpage.
There may have been some 'infection' on that site in the past.
and other reasons.
They are just being careful and looking after you, sometimes they are too careful - but they are trying to look after people who don't know much about computers and computer scams.
I use Malwarebytes Bowser Guard on Firefox and get 4 or 5 similar warnings everyday;.
It depends what I am looking at - as a moderator of a few forums I probably see and visit more dodgy stuff than a 'normal' computer user would.
In the end they are just warnings to say:
'<em>that webpage/website has something unusal that we don't like and we think you should avoid it - but it's up to you to decide</em>'.
Of course the only way to decide is to go there and have a look for yourself.
And that's up to you, if you are unsure then don't go there.