There are several signs that can indicate a non-compliant umbrella payroll company. Here are a few things to look out for:

1. Lack of transparency: A non-compliant umbrella payroll company may not be upfront about their fees or the services they provide. They may also be vague about how they handle taxes and national insurance contributions.
2. Unusual payment structures: Some non-compliant umbrella payroll companies may offer payment structures that do not align with standard payroll practices. This could include large advances or upfront payments, or payments that are not made through standard payroll channels.
3. No liability insurance: A compliant umbrella payroll company should provide liability insurance, which protects the contractor in case of legal action taken against them by a client or a third party. If the company does not offer liability insurance, it may be a sign that it is non-compliant.
4. No access to employment benefits: A compliant umbrella payroll company should provide access to employment benefits such as holiday pay and sick pay, If a company does not offer these benefits, it may be a sign that it is non-compliant.
5. No compliance with legal and tax regulations: A compliant umbrella payroll company should follow all legal and tax regulations. If a company does not comply with these regulations, it may be a sign that it is non-compliant.

It is important to do research and due diligence when choosing an umbrella payroll company. Look for companies that have a good reputation, are transparent about their fees and services, and have a track record of compliance with legal and tax regulations. It is always better to be safe than sorry and not to rush into any agreements.