The regional government has said the rest of Line 2 on the Madrid's underground network — the red line on the map, matching Vodafone's corporate colours — will also carry the name of the mobile company for the duration of the three-year contract.

"It is the first time in Europe that an entire metro line has changed its name based on a commercial deal, generating new forms of income," Madrid's town hall said in a statement.

Signs for Sol station will be rebranded as 'Sol Vodafone' from June 1st and signs along the rest of the line will read 'Line 2 Vodafone' from September.

The advertising deal means Madrid Metro will rake in €3 million euros ($3.9 million) over the next three years, raising its advertising revenues by 10 percent.

Vodafone's advertising campaign will reach out to 122,000 passengers who take Line 2 every day. 

But with a total of 635 million Madrid Metro users every year, many other big brands could take advantage of the Town Hall's willingness to sign lucrative advertising contracts.

The Local spoke to Gabriel Rosado, art director for Spanish advertising company Comunica, about what other big brands could compete with Vodafone by sponsoring other Madrid Metro lines based on their matching colours.

Line 3: “As it’s the yellow line, McDonalds, Shell, Ikea or even Post-it are possible candidates.”

Line 9: “Yahoo is the most obvious choice because their logo is purple.”

Line 8: “Vodafone’s competitors T-Mobile would be a suitable candidate but they don’t operate in Spain. Maybe pink brands like Ausonia (Spanish tampon manufacturer) or Barbie are the best bets.”

Line 1: “Twitter, Skype and LinkedIn all have light blue logos to match this line.”

Line 10: “Movistar may be interested in competing against Vodafone by sponsoring the dark blue line. It also has a lot more stops than the red line so they’d have a bigger reach. Otherwise there’s Facebook, HP or Michelin.”

Line 7: “It’s orange, so have a guess! That’s another mobile operator that may be interested in competing against Vodafone in the underground advertising world.”

Line 5: “It's a green line so BP is the best bet.”