There are two places to see if a Company is being Monitored. The first is in the list of Companies in your Monitoring Portfolios, and the second is in the Company Report. 

Monitoring Portfolios: 

Within your Monitoring Portfolios section, you can see the list of companies that are being monitored. You can change the Portfolio you're viewing in the right-hand drop down, the list of companies monitored in each portfolio will then update accordingly. Within this list, you can see both portfolios you have created, and portfolios that have been shared with you. If a portfolio has been shared with you, then it will have an icon next to the portfolio name. 

Company Reports: 

You can also see if a company is Monitored in the Company Report. If you have Automatic Monitoring enabled, any company report that you view will be added to your Default Monitoring Portfolio. Companies will show up as Monitored in Company Reports for both Portfolios that you own, and Portfolios that have been shared with you. 

Below is an example of a Company Report of a business who is Monitored: 

If you click the green "Monitored" button, you can remove the company from the Portfolio it's added to, or add it to an additional Portfolio (if you have the correct permissions).