In the legal arena a trade mark is in essence a sign for the source or origin of a product (eg branded magazine) or service (eg branded publishing services). In the eyes of the law - the mark sources the trader.
All businesses have trade marks. Their legal status and ease of protection varies for reasons briefly noted here.
In common usage a "trade mark" may be a brand, logo, word or other sign. A trade mark registered in Australia gives its owner the advantage of a monopoly statutory right (ie law made by parliament) to use it in Australia. This legal monopoly right comes into force on registration without evidence of use.
A trade mark used but not registered in Australia still attracts some legal protection. For unregistered brands it is a good idea to apply the TM notice (ie ™) where appropriate. Only registered trade marks can use the R in a circle notice (ie ®).
However, a practical consequence is that a person's claim to exclusive use rights (eg to a magazine's title or masthead) in an unregistered trade mark is only as good as the evidence that can be marshalled to support that claim. The evidence is needed to found the exist that the rights exist because they would be recognised by common law (ie law made by judges). In contrast, a registered trade mark is recognised by statutory law (ie law made by parliament) as well as common law.
A great deal more time, hence expense, is usually involved in preparing a letter of demand to require someone to stop use of an unregistered trade mark. In this context rreliance on common law is more expensive.
To make the demand letter persuasive (especially when read by another lawyer) it is best to marshal a great deal of evidence of use of the unregistered trade mark so as to maximise the available common law threat. For the demand letter this evidence typically covers a great deal of information, it's like telling the life story of the brand covering:
the person, company or enterprise which used the mark, eg owner, licensee or someone else
the date of first use of the mark
the extent of the geographic territory in which it has been used
the products or services for which it has been used
the overlap between all the above and the mark and use by the claimed infringer
A registered trade mark can reduce the time, expense and even need for items 1 to 5. Reference to a trade mark number tells the infringer the trade mark owner's statute-backed claim. Instead of telling a life story, you can in some instrances just point to the trade mark's profile in the official Australian Trade Marks Register.
Simply stated, in the long run the legal costs for protection of a registered trade mark are often lower than for an unregistered trade mark.