If the negative SEO aims to reduce your search traffic, then apparently it will just do that.

You will notice a sudden drop in your search traffic; this can be a symbol provided you haven’t been doing anything dodgy yourself.

The attack can be in the form of a manual penalty notification.

There are two types of penalties; manual and algorithmic.

A drop in traffic and ranking can notice an algorithmic penalty.

However, for a manual penalty; you will receive a message from Google in which they will mention taking action against your site.

A drop in individual keyword rankings can identify another symbol for a hit by negative SEO.

Use Ahref’s rank tracker to keep an eye on the movement of your top and essential keywords.

Add the words on the tool and see how they’ve moved up and down on the SERPs over time.

Spam links can also be a symbol for negative SEO.

How to deal with spam links:
Go to Ahref’s. Go to Alerts > Backlinks > Add alert > Enter domain > Set frequency > Add
A sudden influx of suspicious links can highlight a negative SEO attack.

There can be fake link removal requests, which can also be a source for a negative SEO attack. These can hurt your site.

Use Ahref’s backlinks alert to tackle the issue.

Use Google Analytics to see the:
 Bounce rate stability
 Session duration
 Search console and landing pages
 Site speed

With the confirmation of the negative SEO attack, here is what you can do:

Find contact information for sites with the bad links.

Send an email to the owner and request for the removal of the link.

Use google webmaster, Tools or Link detox to create a document with a list of negative SEOs.

Along with the file, visit Google Disavow links and submit the document.

Invest in a backlink monitoring tool.