Over recent days new markings have appeared on Russian vehicles placed close to the Ukrainian border.
An expert has said the painted signs are normally used to communicate where military units are headed in battle and are usually only put on equipment shortly before combat.
Sky News has seen on images emerging out of the region at least 10 different types of symbol being used by the Russian forces, some of which only seem to be appearing in certain locations.
So what do these symbols mean?
The image below shows a distinctive ‘Z’ in a square box painted on a truck.
This type of symbol has appeared on a host of vehicles near the city of Belgorod in Russia, less than 20 miles from the Ukrainian border and 45 miles from the Ukrainian city of Kharkiv.
It is feared Kharkiv, a city of 1.4 million people, could be targeted if Russia launches a fuller invasion.
See live updates on the Ukraine crisis
Variations of the symbol have also emerged, such as in these images where trucks have the ‘Z’ symbol painted inside a triangle rather than a square.
In another video posted on 22 February a tank can be seen painted with a triangle and two lines on its side, and a larger version of the symbol on its front that could be identified from the air.
A number of other symbols have also been seen on vehicles, including in places like Crimea.
It is suspected that the markings are likely to have two purposes: to identify vehicles as Russian, so they don’t get targeted by other Russian forces in ‘friendly fire’, and to denote attack groups and their objectives.
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Professor Michael Clarke, former director of the defence think tank RUSI, said the symbols are likely to be connected to the geographic location of where the units are destined for in an offensive.
He told Sky News: “Often these symbols will be location based – they will be communicating where a unit is heading. If they were only to mark the vehicles as being Russian, you could just use one symbol.
“The fact that they are different tells you more – they are probably signs which tell you which units are heading to the northeast or northwest of a district, for example.”
Professor Clarke said the use of these types of symbols is common in war. US forces used chevrons to denote different companies in Iraq.
He also said they are normally only used shortly before any fighting in case the opposing force begins to copy the markings.
It is further evidence of the continued tension along the border with Ukraine as the latest satellite imagery shows that a field hospital has been erected near Belgorod, the area where many of the videos of this marked equipment have been recorded.
The precise meaning of the symbols is as yet unknown. Deciphering their purpose will no doubt form an important part of the assessments being made by US and UK military intelligence.
Other key developments in Ukraine:
• Putin has gone ‘full tonto’, UK defence secretary says
• Ukrainian president calls up army reservists
• White House says Biden-Putin summit ‘not in the plans’ anymore
• US Secretary of State Blinken cancels talks with Russia’s Foreign Minister Lavrov
• Australia, Canada and Japan join other nations in sanctioning Russia
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